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- Zlatkovikj, Milan
(author)
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Analysing the transient operation of the boiler and the TES tank for improving the flexibility in biomass CHP
- 2023
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Doctoral thesis (other academic/artistic)abstract
- The uncertainty in the energy systems due to the continuously growing share of variable renewable energy sources (VRES) increases the requirements for flexibility. From the multiple mechanisms to improve flexibility, biomass-fired combined heat and power plants (CHPs) have gained attention due to their sustainability and high efficiency. CHPs with thermal energy storage (TES) can provide flexibility by adjusting their power to heat ratio. The aim of this thesis is to analyse the transient operation of the boiler and the TES tank in biomass CHP, based on dynamic modelling. The commonly applied proportional integral (PI) controller has numerous limitations for complex multivariable processes like boilers. Advanced controller (model predictive control (MPC)) and additional sensor (feed-forward (FF)) are proposed to improve the control of the process. For the TES tank, the dynamic model is used to investigate the influence of the state of charge, flowrates and temperatures used on its charge and discharge rates. Results show that FF MPC can allow for more accurate transient control of the boiler, which will result in a faster response rate of the CHP to changes in supply and demand. The assessment of the TES tank operation enabled a mapping of the range of charge and discharge rates and the factors that can influence it. This knowledge can be utilised to conduct accurate additional studies on the role of TES in a CHP flexible operation.
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| 2. |
- Zlatkovikj, Milan, et al.
(author)
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Development of feed-forward model predictive control for applications in biomass bubbling fluidized bed boilers
- 2022
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In: Journal of Process Control. - : ELSEVIER SCI LTD. - 0959-1524 .- 1873-2771. ; 115, s. 167-180
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Journal article (peer-reviewed)abstract
- In order to accommodate more intermittent renewable energy sources, biomass fueled combined heat and power plants (bio-CHPs) can contribute towards sustainable and flexible energy systems. However, the varying properties of biomass, such as moisture contents and heating values, can clearly affect the combustion in boilers, which further affects the flexibility provided by bio-CHPs. In order to achieve better control, this paper proposes a feed-forward model predictive controller (FF MPC) to handle the variation of biomass properties. A dynamic model was built in Dymola to simulate the performance of a bubbling fluidized bed boiler, which was validated against the real operation data. Based on the simulation, the key manipulated variables were optimized for the given controlled variables. The advantages of the proposed FF MPC were demonstrated through comparisons with proportional- integral (PI), FF PI and MPC. The results of FF MPC show the best performance, such as the lowest magnitude of fluctuations for 3 outputs (thermal load, steam and fluidized bed temperature), and the most stable operation. Consequently, FF MPC can potentially increase the electricity generation and further lead to an economic benefit. Using one week in winter as an example, compared to PI, FF PI and MPC, FF MPC can generate more electricity and improve revenues by 14.77 MWh/590 =C, 4.1 MWh/164 =C and 5.03 MWh/211.2 =C respectively.
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| 3. |
- Zlatkovikj, Milan, et al.
(author)
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Dynamic model for large scale hot water storage tank
- 2023
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In: Energy proceedings. - : Applied Energy Innovation Institute (AEii). ; 30, s. 1-6
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Journal article (peer-reviewed)abstract
- Due to the growing share of intermittent renewable energy sources (RES), the requirement for flexibility in the energy system is increasing to balance the generation and demand of electricity. It has been well recognized that Combined heat and power plants (CHPs) can contribute towards improved flexibility in the energy system. Thermal energy storage (TES), using hot water as working fluid, is a commonly integrated in CHPs, which allows for decoupling of heat and electricity generation. It has been verified that proper control of the operation of TES can improve the flexibility provided by CHP. The development of advanced control system relies on accurate dynamic modeling of TES. In this work, a one-dimension (1D) dynamic model for large scale TES is developed in Dymola, based on mass and energy balances. It is validated against the operational data from a real CHP plant. Results show that the model can capture the dynamic variation in the operation of the TES energy content with maximum deviations of 6.5% from the maximum value.
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| 4. |
- Zlatkovikj, Milan, et al.
(author)
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Influence of fuel properties on the performance of the feed forward model predictive control (FF MPC) for biomass boilers
- 2023
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In: Energy Proceedings. - : Scanditale AB. - 2004-2965. ; 32, s. 1-6
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Journal article (peer-reviewed)abstract
- The growing share of renewable energy sources drives the need for increased flexibility in the energy systems. The flexibility provision from thermal plants is limited by the boiler’s thermal inertia as a bottleneck. Advanced controllers, such as model predictive control (MPC), have been identified as potential flexibility enablers. Fuel properties are crucial input for controllers. This work investigated the feasibility of using the properties obtained online by using near infrared spectroscopy based soft sensor to further improve the control performance. The performance of the existing proportional integral (PI) controller is compared with those of 2 feed forward (FF) MPC controllers. Both FF MPCs have significant improvement compared to PI controller and the FF MPC based on the full elemental composition shows the best performance due to more complete fuel information. There is a potential for revenues improvement with advanced control up to 1050 euros for one operation day.
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| 5. |
- Zlatkovikj, Milan, et al.
(author)
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Influence of the transient operation of a large-scale thermal energy storage system on the flexibility provided by CHP plants
- 2023
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In: e-Prime - Advances in Electrical Engineering, Electronics and Energy. - : Elsevier Ltd. - 2772-6711. ; 4
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Journal article (peer-reviewed)abstract
- Among many technical options to improve the flexibility in combined heat and power (CHP) plants, thermal energy storage (TES) has attracted the most attention with its high applicability and benefit. Previous studies normally adopted a simplified approach for modelling a TES system, which assumes the optimized charged or discharged rate of heat can always be realized within the rated capacity. However, this may yield unfeasible results as the charging and discharging rates are dependent on the dynamic status of a TES, such as the state of charge (SOC) and water temperature, and the water flowrate for charging and discharging. In order to consider the transient operation of a TES, a 1D dynamic model was developed and validated against measured data from a real CHP plant. To analyze the dynamic performance of a TES, two key performance indicators (KPI), the maximum charging/discharging rate (C/D-ratemax) and the constant maximum charging/discharging rate that can be maintained constantly for one hour (CC/CD-ratemax) were employed. By doing simulations, it has been found that the CC/CD-ratemax was lower than the C/D-ratemax for most given SOCs of the studied TES. The developed model was also used to examine the optimized operation of a TES for providing flexibility. Some unfeasible results have been identified, as the optimized hourly charging/discharging rates were constrained by the CC/CD-ratemax. Therefore, it is of great importance to integrate a detailed dynamic model when optimizing the dispatch of electricity and heat for a CHP plant.
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