Many nations are struggling to phase out coal. Some, like China, are heavily dependent on it, and have more plants in the pipeline to ensure energy security and keep prices low. In other words, a lot of coal will remain in operation for the medium term. Given that, it makes sense to make them more efficient while they are in use. Daisy Chi at ECECP looks at a new set of tools – the Plant Efficiency Toolbox (PET) – that can analyse and optimise a coal plant’s performance and thereby cut coal use, costs and emissions. The tools are easy enough for plant engineers to use, inexpensive, and give results quickly. The main focus is on the boilers and cooling towers, the two major components that generate almost all plant losses and 100% of emissions. After inputting boiler data, the optimisation results are generated in seconds. For the more complex cooling towers, AI-driven mobile units, alongside an advanced algorithm, are deployed within the cooling tower to collect data. PET is also developing tools to enable plant boiler bottom ash removal and unburned ash afterburning technology, and open the door to co-firing processed waste. Chi points at case studies in Indonesia and Europe, and estimates that complete implementation of PET in China, including waste co-firing, could reduce coal usage by up to 10%.
China’s coal dependency
China’s coal-fired generation plants generate almost 60% of the country’s power and more than 40% of carbon emissions. Their remit is to cut emissions even as they maintain output to secure the country’s power supplies.
Yet the coal price, which generally accounts for a majority of 70-80% cost for a power plant, has had a roller coaster year. By Oct 15th, the 5500kcal (22.9MJ/kg) coal stock price reached a historic high at more than CNY 2200 (USD 342/t), more than double the price of the same period of last year.
As the coal price skyrockets and the authorities retain the low benchmark power prices, most coal-fired generation companies find now that the more power they produce, the more money they lose. Some plant operators report that for every single unit of power produced, they lose CNY 7-8 cents (USD 1.1-1.2 cents) at the current market coal price, which translates into over more than USD 155,000 loss per day if they run in full capacity.
This dismal picture is confirmed by recent industry figures showing that 70% of coal-fired assets in big generation groups are running at a deficit, with no prospect of an improvement in the near term. In early September, 11 coal-fired power companies took the unprecedented step of requesting a rise in electricity prices in order to avoid bankruptcy. The squeeze on coal supplies to coal-fired power plants is causing severe power shortages across China, affecting millions.
There is no turning back from China’s carbon neutrality targets: coal’s current dominance will continue to weaken and shift towards flexible power sources. Yet in the near term, installed coal fired capacity is still set to grow in order to meet rising power demand and to safeguard supply. In addition to its 1,079 GW existing coal power generating capacity, China has over 357 GW more in the pipeline.
Top of the agenda in the power sector is the task of making traditional coal-fired units environmentally friendly, with higher power generation efficiency and lower energy consumption. China has already moved to shut down underperforming units and implement ultra-low emission and energy-saving measures in existing assets. Statistics show that by the end of 2020, 950 GW of China’s coal power capacity had been upgraded, affecting about 89% of existing assets.
The emission of major pollutants from coal-fired power plants, as well as average coal consumption for power generation, have both seen a steady decline over the past few years (the latter has dropped from nearly 400g per kWh in 2000 to 304.9g per kWh in 2020). Nevertheless, in 2020 Chinese coal power plants consumed nearly 1.7 billion tonnes of coal.
Dr Zeljko Warga, business development associate of IBE, the oldest industrial engineering company in Slovenia founded in 1949, believes there is huge potential for China’s coal-fired power plants to improve their efficiency. He has co-developed an innovative Plant Efficiency Toolbox (PET) for coal-fired power plants that can cut coal usage, and so reduce operating costs and emissions. The PET relates to the two major plant components, the boiler and cooling tower, which generate nearly all plant losses and all emissions.
Boiler efficiency optimisation
The boiler is the primary plant component, and its performance directly determines the plant operating efficiency. This in turn affects the overall plant economics and its environmental footprint. ‘To secure better performance, the key is to know details on what goes on in the boiler from heat transfer point of view’ notes Dr Warga.
He has developed online boiler heat transfer calculation software for everyday engineering use. This web-based tool can conduct thermodynamic calculations and simulate the impact on boiler performance of operating parameter changes (combustion quality, feed water temperature, steam pressure, etc.) fuel composition (coal change and coal blending, alternative fuel addition) and boiler internal geometry (use of refractory in furnace, for instance).
Boiler-related calculations are not new to plant operators. However, existing software tools are complex and can only be operated by specialist external companies, whose services can be very costly (in the region of USD 30k-60K) and time-consuming (a specialist survey can take weeks).
Warga’s software is specially designed for use by plant engineers with basic theoretical and practical knowledge about heat transfer in boilers, and is accessible to anyone. The user only needs to enter boiler internal geometry information, fuel composition and operational readings, and the calculations will be carried out in the background in a matter of seconds. The software then generates a clear picture of what is going on inside the boiler and how changes in operating parameters and geometry affect the outcome, steam production and efficiency. ‘This is the first time such a tool has been publicly available to engineers to serve their needs on a 24/7 basis,’ says Warga.
Warga’s team has gone a step further. Not content with knowing the optimisation potential, they also provide an innovative boiler tuning expertise which means they can fine tune a boiler to get the desired results.
Case study: Indonesia
In late 2015 the team won an advanced combustion tuning project funded by the United Nations Industrial Development Organisation (UNIDO) at a coal-fired power plant in Indonesia. The candidate boiler was a 600 MW boiler (1,900 t/h steam at 190 bar) and the project was completed in June 2016. The Babcock & Wilcox Canada boiler was already very well maintained, and had sustained commissioned values from September 1997, a remarkable achievement. Nevertheless, there was still room for improvement.
Once the recommendations were adopted, the boiler saw savings of around 35,000 t/yr of reduced coal usage, 67.000 t/yr in CO2 emissions reduction, and 458 t/yr (all metric tonnes) in SO2 emissions reduction.
‘To bring this into perspective, in 2014, ABB tuned a boiler (Unit 4) at the same location and achieved 0.33% energy savings. When we took on combustion tuning in 2016, we achieved around 0.7% boiler efficiency increase at nominal load, and more than twice as much at 66% load,’ argues Warga.
Even more boiler tuning potential was detected following subsequent boiler thermodynamic calculations and simulations with Warga’s software.
The plant’s total coal usage reduction potential (extrapolated to the plant’s eight boilers, 4,025 MW in total) was found to be around half a million tonnes, representing more than 900,000 tonnes of CO2 reductions. This is achievable without capital investment or boiler stoppage, according to Warga. In total, around 3.5% coal usage and consequently this much CO2 emissions reduction potential was detected.
‘Based on these results, we have good reason to believe that if such potential exists in what is touted as best set and operated plant in a country, there is significant potential elsewhere,’ declares Warga.
Cooling tower efficiency: neglected potential
Another key component of a coal-fired power plant that could benefit from further efficiency improvement is the cooling tower. Its improvement potential is often overlooked. ‘Cooling towers in most cases do not operate optimally because evaluation methods are largely statistical due to practical limitations: their giant size and thousands of water-rinsed tubes make manual data collection impossible. This way, some areas in need of attention are left out. Losses from an improperly maintained cooling tower can amount to millions of dollars per year for a single plant,’ says Warga. ‘The trick is to be able to quickly locate areas inside the cooling tower where conditions depart from the optimum operation point.’
The new technology employs AI-driven mobile units alongside an advanced algorithm that are programmed and deployed within the cooling tower to collect data for performance evaluation and to identify anomalous areas left out by statistical methods. The potential gain from eliminating those anomalous areas is calculated and a baseline is set so that operators can be alerted when any deviation is detected. The option for this technology is included in the PET.
Demonstrations of the technology have been carried out at several European sites. ‘The results are encouraging. A system efficiency increase of between 0.3% and 1% (0.65% on average) was observed even in the case of equipment that has been properly and regularly inspected and maintained,’ reports Warga. The cost of the service can be recouped within weeks.
An ‘All-at-Once’ solution
Boiler and cooling tower operation evaluation, and consequently plant performance improvement, is normally undertaken by specialist service companies who keep the know-how to themselves. Warga believes that most of the optimisation work can be carried out by trained plant staff, so yielding much quicker results nationwide. ‘Our idea is to equip plant staff with the know-how through training. It is always better to teach a man how to catch the fish than to give him a fish.’
Warga’s ‘All-at-Once’ strategy provides a mass plant staff training and technology transfer that enables widespread implementation of the PET. ‘It makes little sense to handle a single plant at a time, when the clock is already ticking for tackling climate change,’ he says. In his view, this strategy offers the best way to deploy the software and knowhow more widely. The economic gains from adopting the package can then be used to invest in environmental and technological upgrades or to recoup costs.
China has the biggest potential
The PET was first brought to public attention at a coal power themed workshop in Vietnam, organised by the Centre for Sustainable Carbon, formerly the Clean Coal Centre in London. ‘We’ve successfully introduced the software in Vietnam. But the country that has the most potential and stands to benefit most from the PET is of course China!’ states Warga. He presented it to a Chinese audience for the first time at an innovation-themed event held by EU-China Energy Cooperation Platform (ECECP) earlier in 2021.
With China’s coal-fired plant operators facing soaring coal prices and demands to reduce emissions, the PET offers the potential to ease that pressure with less external effort and minimum capital outlay.
‘We firmly believe the All-at-Once strategy can be replicated in China. Countries like China and Vietnam possess certain institutional advantages for deployment and therefore can more easily reap the benefit from unified action,’ says Warga.
The PET is set to improve further with advanced, yet simple and cost effective, plant boiler bottom ash removal and unburned ash afterburning technology. This has also the potential to reduce emission further by co-firing processed communal waste (RDF) in power plants to replace part of the fuels, which not only can reduce coal usage but also handle the municipal waste problem at the same time without the need to build controversial and expensive incinerators.
Cutting China’s coal use by up to 10%
Warga estimates that complete implementation of PET in China’s coal-fired power plants, including RDF co-firing, could reduce coal usage by up to 10%, which translates to a staggering 170 million tonnes a year, given 1.7 billion tonnes annual usage, and more than 320 million tonnes reduction in CO2 emissions – five times more than Three Gorges Dam’s contribution in 2020.
With the coal price soaring, a climate crisis, and countries worldwide rushing to implement policies and legislation to cut emissions, innovative solutions to optimise plant performance and efficiency are needed more than ever to cut fuel use and reduce coal’s environmental footprint. Warga’s PET shows what can be achieved just through effective management of existing assets.
This article was first published in the EU-China Energy Magazine 2021 Autumn Issue, available in English and Chinese, and is published here with permission
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