Bord na Móna’s Edenderry Power Plant in Ireland has reduced its NOx emissions with an advanced process control application, Valmet DNA Combustion Manager.
Just like many large combustion plants in the EU, the Edenderry Power Plant is faced with the challenge to lower its NOx emissions, and meet a new projected 220 mg/Nm3 daily limit and 180 mg/Nm3 yearly limit defined by the Industrial Emissions Directive.
Started up in 2000, the 128 MWe plant generates electricity by co-firing with a typical energy mix of 60% peat and 40% biomass. Co-firing with biomass has produced impressive results and reduced the plant’s carbon footprint significantly over the years. Now the focus is on NOx emissions.
“With a reduction in our emissions coming into force during 2020, we needed to start a program for emission reduction and product selection. Through conversations with Valmet’s Service Manager Nigel Earp and Business Development Manager Chris Heywood, we understood that Valmet had the ability to develop boiler controls which could improve boiler efficiency as well as lower NOx and CO emissions,” says Padraig Nolan, Thermal Plant Manager at Edenderry.
The BFB boiler was built by Valmet (Kvaerner at the time) in 1999, and cooperation has continued over the years in various improvement projects. “Valmet has proven to be a reliable supplier of services and always stayed with us to ensure the service promised by them was delivered and if possible exceeding their original promises. The automation solution was the first installment of our de-NOx program, effectively picking up the low hanging fruit,” Padraig points out.
For 18 years the plant adjusted set points for fuel and air staging manually. These parameters could be changed on the DCS by the operators. With the varied fuel in the peat and biomass mix, however, it would be impossible for an operator to keep changing these parameters to maximize the plant efficiency.
Evaluating improvement potential
The NOx project started in 2017 with Valmet carrying out a process improvement study to evaluate the potential for emissions reduction with Valmet DNA Combustion Manager.
In early 2018, this advanced process control application for optimized combustion was installed in the plant’s existing Valmet DNA automation system. It is based on Industrial Internet and designed for bubbling fluidized bed (BFB), circulating fluidized bed (CFB) and waste-to-energy boilers to manage the combustion process against variations in production, fuel amount, fuel quality and combustion circumstances.
“The project team worked very effectively and efficiently. We had the advantage of Valmet working with the original DCS system which minimized any potential complications of introducing unfamiliar packages,” Padraig says. “The project duration was accurate. We could see improvements as soon as the improved controls were implemented. Over the next few months, Valmet made some adjustments based on results and operator experience which could be completed while the unit was online.”
Lower CO levels and NOx emissions
The plant is very pleased with the results. “Now with the fuzzy logic in place, the controllers are adjusting constantly, working together to ensure we have the fuel in the right place and air staging at the most optimal point. CO levels and NOx emissions are reduced, and this is the case all through the load range of the unit. As our minimum load is 35% of our maximal output, efficiency improvement and NOx reduction at the lower load is significant. The solution is reliable and with the tweaks that we work together on, the improvements are ongoing,” Padraig continues.
The main benefits for the process include NOx and CO reduction, improved bed temperature control and higher efficiency. The 30% NOx reduction – 320 tons per year – equals the emissions of approximately 100,000 diesel cars.
Picture 1. Average NOx level as function of boiler load before optimization project (including verification points used for estimating tuning potential).
Picture 2. Average NOx level as function of boiler load after optimization project. NOx level reduced 20-30 %. At medium load range emission limits are met without the need for secondary control measures. At minimum and maximum load, the general NOx level is sufficiently reduced for the emission limit to be met utilizing the upcoming SNCR system.
“This project is a good example of utilizing combustion optimization and advanced control systems as part of the Best Available Technology (BAT) to meet more stringent emission and efficiency requirements,” adds Matts Almark, Product Manager, Power Plant APC, Valmet.
Results exceed expectations
Valmet’s expertise in control technology met the plant’s needs spot on. Padraig goes on: “The team displayed a deep understanding of our process and equipment. This gave us comfort in allowing the guys to make the adjustments during the test phase. The results speak for themselves; we have seen results that consistently exceed the original expected improvement which means the second phase of NOx reduction, which will be in place towards the end of this year, will have an easier task to achieve our new limit.”
NOx reduction was the plant’s number one priority for this project. “We never expected to achieve the new 2020 limit but had hoped to make improvements which meant the next phase of NOx reduction could be achieved. With the high capital cost associated with an SCR system and the fact we have biomass in the fuel stream, it meant an SCR was not an option for ourselves so we are currently installing an SNCR system which will complement the Valmet solution in achieving our target. Process stability has improved with the improved controls.”
Padraig thinks highly of the cooperation with Valmet. “We found the Valmet guys to be open to sharing information and listening to the experience of our teams which fed into the testing and programing of the package. We have comfort in knowing that the team review the performance of the solution and are making recommendations based on the findings.”
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