Biomass-fired Organic Rankine Cycle Research Articles

Dynamic behaviour and performance evaluation of a biomass-fired organic Rankine cycle combined heat and power (ORC-CHP) system under different control strategies

The dynamic behaviour and performance evaluation of a biomass-fired organic Rankine cycle combined heat and power (ORC-CHP) system under two different control strategies are investigated in this study. The dynamic model is established, while the dynamic characteristics of key operating parameters (superheat degree, evaporating pressure and mass flow rate) with the step change of heat source temperature are examined. The effects of controlled superheat degree and controlled expander shaft work on dynamic behaviours of thermodynamic, economic and environmental performance are discussed and compared under different control methods (feedforward active control, PID passive control and combined control). Results indicate that the superheat degree is significantly influenced by the heat source temperature under the without control strategy, with the variation reaching 8.4 K. The combined control method exhibits the best control performance with overshoot and control response times of 1.2 K and 12.3 s, respectively. Compared to without control, the expander shaft work and ORC thermal efficiency of the control strategy of superheat degree increase by 3.2 kW and 0.8 %, while that of the control strategy of expander shaft work increase by 1.0 kW and 0.3 %, respectively. The control strategy of superheat degree presents a significant improvement in the economic and environmental performance of the biomass-fired ORC-CHP system. This study is expected to provide better guidance for the practical operation and control of biomass-fired ORC-CHP systems.

Parametric analysis and multi-objective optimization of biomass-fired organic Rankine cycle system combined heat and power under three operation strategies

Biomass-fired organic Rankine cycle (ORC) systems for combined heat and power (CHP) generation are a feasible technology to provide carbon-neutral power production. In this study, the parametric analysis and multi-objective optimization of a biomass-fired ORC-CHP system under three operation strategies are conducted. The thermodynamic, exergoeconomic, environmental and sustainability models are established, while the effects of seven operation parameters on exergy efficiency (ηex), unit cost of exergy (UCE), equivalent carbon emission (ECE) and ecological life cycle cost (ELCC) are examined. A further four-objective optimization problem is addressed using NSGA-II and the Pareto-optimal solutions for the three operation strategies are derived and compared. The results indicate that evaporation temperature, condensation temperature and heat source inlet temperature present positive effects on ηex and UCE, whereas opposite effects are imposed by degree of superheat and pinch point temperature difference. System B yields a 0.21% higher ηex and a 0.41 tons higher CO2,eq than system C. The Pareto-optimal solutions of ηex, UCE, ECE and ELCC for system A using TOPSIS decision-making are 12.380%, 0.183 $/kWh, 10.250 tons CO2,eq, and 13.677 × 10−3 $/kWh, respectively. System A may be regarded as the preferred operation strategy for biomass-fired ORC-CHP systems due to its moderate performance.

Recent Advances in Small-Scale Carbon Capture Systems for Micro-Combined Heat and Power Applications

To restrict global warming and relieve climate change, the world economy requires to decarbonize and reduce carbon dioxide (CO2) emissions to net-zero by mid-century. Carbon capture and storage (CCS), and carbon capture and utilization (CCU), by which CO2 emissions are captured from sources such as fossil power generation and combustion processes, and further either reused or stored, are recognized worldwide as key technologies for global warming mitigation. This paper provides a review of the latest published literature on small-scale carbon capture (CC) systems as applied in micro combined heat and power cogeneration systems for use in buildings. Previous studies have investigated a variety of small- or micro-scale combined heat and power configurations defined by their prime mover for CC integration. These include the micro gas turbine, the hybrid micro gas turbine and solid-state fuel cell system, and the biomass-fired organic Rankine cycle, all of which have been coupled with a post-combustion, amine-based absorption plant. After these configurations are defined, their performance is discussed. Considerations for optimizing the overall system parameters are identified using the same sources. The paper considers optimization of modifications to the micro gas turbine cycles with exhaust gas recirculation, humidification, and more advanced energy integration for optimal use of waste heat. Related investigations are based largely on numerical studies, with some preliminary experimental work undertaken on the Turbec T100 micro gas turbine. A brief survey is presented of some additional topics, including storage and utilization options, commercially available CC technologies, and direct atmospheric capture. Based on the available literature, it was found that carbon capture for small-scale systems introduces a large energy penalty due to the low concentration of CO2 in exhaust gases. Further development is required to decrease the energy loss from CC for economic feasibility on a small scale. For the micro gas turbine, exhaust gas recirculation, selective gas recirculation, and humidification were shown to improve overall system economic performance and efficiency. However, the highest global efficiencies were achieved by leveraging turbine exhaust waste heat to reduce the thermal energy requirement for solvent regeneration in the CC plant during low- or zero-heating loads. It was shown that although humidification cycles improved micro gas turbine cycle efficiencies, this may not be the best option to improve global efficiency if turbine waste heat is properly leveraged based on heating demands. The biomass-organic Rankine cycle and hybrid micro gas turbine, and solid-state fuel cell systems with CC, are in early developmental stages and require more research to assess their feasibility. However, the hybrid micro gas turbine and solid-state fuel cell energy system with CC was shown numerically to reach high global efficiency (51.4% LHV). It was also shown that the biomass-fired organic Rankine cycle system could result in negative emissions when coupled with a CC plant. In terms of costs, it was found that utilization through enhanced oil recovery was a promising strategy to offset the cost of carbon capture. Direct atmospheric capture was determined to be less economically feasible than capture from concentrated point sources; however, it has the benefit of negative carbon emissions.

Techno-economic assessment of a small-scale biomass ORC-CHP for district heating

The present work focuses on the techno-economic assessment of a small-scale (1000 kWth) biomass-fired Organic Rankine Cycle (ORC) plant for combined heat and power (CHP) generation coupled to a district heating network. The ORC is designed to maximize its nominal installed power for several natural refrigerants and R1233zd. A part-load model is developed to determine the plant’s annual electrical energy and heating output when covering the heating loads of energy-efficient buildings of communities of various sizes in three cities representing the main climate zones of Europe, namely Athens, Berlin and Helsinki, with a peak load of up to about 10,200 kWth. A series of parametric analyses are carried out to investigate the plant cost-effectiveness under different assumptions. The plant’s economic performance is very low, as only under the combined existence of multiple favorable factors (high electricity and heat prices, low biomass cost) and long operating hours it is possible to achieve discount payback periods of at least 5–7 years. Three factors that result in the unsatisfactory economic performance of the plant are its high specific cost, reduced operating hours and reduced electricity production, which is caused by the maximum temperature limitation of screw expanders at the investigated scale.

Techno-economic optimization of ORC system structure, size and working fluid within biomass-fired municipal cogeneration plant retrofitting project

This paper continues discussion on financial viability and design optimisation of biomass-fired Organic Rankine Cycle (ORC) Combined Heat and Power (CHP) systems. It examines influence of such decision variables as ORC system rated electric power output, architecture and working fluid. The considered ORC system structures are simple, regenerative and regenerative cycle with split heat exchanger. Eight working fluids are considered, namely: MM, MDM, MD2M, D4, D5, toluene, ethylbenzene, and cyclohexane. The system was modelled and simulated using Ebsilon® Professional software. Sample project is assessed in terms of power generation efficiency, Primary Energy Savings (PES), and financial indicators, such as Net Present Value (NPV) and Internal Rate of Return (IRR). Results revealed considerable differences in optimal power output. The optimal value of the ORC generator power output in terms of NPV is within the range from 1000 to 2600 kW depending on the system configuration and the working fluid. In terms of IRR the optimal rated power is between 750 and 1400 kW. The highest values of nominal rated power output have been obtained for ethylbenzene. What is more, the economic indicators get higher values for hydrocarbons than for silicone oils, which are nowadays widely used in biomass fired ORC systems.

Thermodynamic analysis and economic assessment of biomass-fired organic Rankine cycle combined heat and power system integrated with CO2 capture

Biomass-fired combined heat and power system with electric scale below 500 kW down to 100 kW (or even lower) constitutes an emerging distributed market. Organic Rankine cycle coupled with biomass combustion boiler is an appealing and promising technology for small-scale combined heat and power systems. In this paper, a biomass-fired ORC-CHP system integrated with monoethanolamine-based CO2 capture is designed, in which the pressurized hot water is used as heat source for ORC system and the condensation heat can be fully utilized to supply domestic hot water. The pinch point temperature difference analytic method is adopted to investigate thermodynamic performance. Thermodynamic analysis, parametric optimization and economic assessment with a special focus on CO2 capture have been conducted for eleven candidate working fluids. Results show that an optimal evaporation temperature exists with a given pressure ratio in the ORC system. The optimal heat source temperature for ORC system in the bioenergy system can be obtained by optimizing the total investment, dynamic payback period and profit ratio of investment, and the condensation temperature is also optimized using a thermo-economic evaluation. The biomass-fired ORC-CHP system with cyclopentane presents excellent thermodynamic performance with the highest primary energy saving ratio, the lowest net power indicator and levelized energy cost, followed by R141b, R113, R123 and Pentane; while HFE7000 achieving the largest profit ratio of investment and net present value is the best preferable working fluid in terms of economic assessment, followed by R1233zd, isobutane, isopentane and R113. The bioenergy system with optimized parameters is thermodynamically feasible and economically attractive, eco-friendly with negative carbon dioxide emissions thanks to the CO2 capture.

Options for using solid oxide fuel cell technology in complex integrated biomass gasification cogeneration plants

The aim of this paper is to draw readers' attention to potential new technological solutions for effective utilisation of dispersed biomass resources in distributed community-scale applications. In the paper conceptual system, that consists of allothermal wood gasifier, solid oxide fuel cell (SOFC), internal combustion piston engine (ICE) and Organic Rankine Cycle (ORC) for waste heat recovery, is proposed. Configuration of such systems is nowadays possible due to availability individual small-scale energy conversion technologies that can be integrated into complex structures. In the studied case the anode exhaust gas of the syngas fired SOFC module, that still contains combustible gases, is considered a secondary fuel for a bottoming ICE. The ORC cycle module is driven by the heat recovered from process gas coolers as well as from SOFC cathode and ICE exhaust gases. The system has been theoretically evaluated in terms of energy conversion efficiency and profitability using thermodynamic and economic analysis. Relevant robust mathematical models of key components have been developed. Through the modelling the most important performance parameters are addressed. Electric power of the sample system is below 1 MW what makes it suitable for utilisation of locally available biomass. Simulations revealed potentially high value of the net biomass energy to electricity conversion efficiency of 37%–40% depending on the ORC cycle configuration. Financial analysis revealed positive values of profitability indices at current level of market prices. The results are compared with a real biomass-fired ORC cogeneration project. The system also addresses issues related to external effects of the project, such as global emission reduction and primary energy savings.

Energy performance and profitability of biomass boilers in the commercial sector: A case study in the UK

Commercial buildings or shopping malls are characterized by large thermal and electrical energy consumptions with high variability of energy demand. Therefore, there is a large interest to explore novel renewable energy generation systems for these applications. A novel flexible configuration of biomass-fired CHP system with organic Rankine cycle (ORC) is here proposed and applied to the case study of food retail buildings in the UK. The proposed configuration adopts a molten salt (MS) circuit to transfer heat from the biomass furnace to the ORC plant. A thermal Energy Storage (TES) is proposed to improve the flexible operation of the plant and reduce the size of the biomass boiler. Molten salts have been preferred to thermal oil as they have no fire risks and low environmental impact and can be used as medium for a Two Tank TES with a “direct heating” scheme. The plant has been analysed using real input data from a biomass boiler installation, conversion efficiency and heat demand from the store. The model is informed by hourly energy costs and electricity feed in tariff in order to define optimal size and operation of the bottoming ORC for the specific case study of large commercial energy end user in the UK. The results show that the use of thermal storage in a biomass-fired ORC plant can improve the boiler efficiency and reduce the biomass consumption in thermal-load following operating mode and increase the investment profitability.

Size optimization of a biomass-fired cogeneration plant CHP/CCHP (Combined heat and power/Combined heat, cooling and power) based on Organic Rankine Cycle for a district network in Spain

This paper presents a methodology to optimize the size (electric power) of a cogeneration plant based on a biomass-fired Organic Rankine Cycle and connected to an existing district heating network, maximizing profitability. First, a model to determine the hourly thermal energy demand profile of a location in Spain has been derived, from open access meteorological data included in Spanish building regulations. Partial load model of an organic Rankine plant has also been obtained to increase the operation hours. These tools have been applied to two locations in Spain with different climatic severities, calculating the optimal size of the plant. The business model does not include subsidies. Calculations show that for population between 10,000 and 20,000 inhabitants the size of the plant ranges from 2 to 9 MWe and the internal rate of return ranges from 6% to 18%. The coverage of the thermal energy demand ranges from 40% to 80%. Regarding the trigeneration mode, it is concluded that cooling is only worth in locations with high summer severity and in full load operation mode, being the optimal size of the plant smaller in trigeneration mode than in cogeneration.

Biomass-fired CHP and heat storage system simulations in existing district heating systems

The installation of a biomass-fired Organic Rankine Cycle (ORC) unit coupled to a heat storage system (HSS) in an existing district heating (DH) system is proposed and analyzed from both energetic and economic point of view. A real DH system is considered as case study, and the optimal layout configuration is investigated varying the size of the components. The analysis is carried out tuning the heat demand dataset obtained from real data of a different existing DH system with a 6-min time step and ten years of operation. The heat demand is used to match the production from different generation units. The overall efficiency of the system, the primary energy savings related to CHP production, as well as the pay back time of the investment are evaluated. Calculations show that for the considered case study the maximum size of the HSS that gives noticeable advantages is 150 m3/MWth. The optimal configuration is different when considering energetic or economic criteria. Moreover, the current Italian incentive tariff on electricity production from renewable sources appears to promote the choice of low efficiency layouts for the case study under consideration.

Experimental investigation of a biomass-fired ORC-based micro-CHP for domestic applications

The ever-increasing global energy demand and the mounting environmental concerns caused by the increasing consumption of fossil fuels call for more and more utilisation of sustainable energy sources such as biomass. Many medium- and large-scale biomass-fired combined heat and power (CHP) plants have been demonstrated and commercialised in many parts of the world, such as several European countries and China. However, few biomass-fuelled micro-scale CHP (1–10kWe) systems suitable for domestic applications have been demonstrated or commercialised. This paper presents the preliminary results of an experimental investigation on the biomass-fired organic Rankine cycle (ORC)-based micro-CHP system currently developed by the authors. The biomass-fired ORC-based micro-CHP system mainly consists of a biomass boiler, an evaporator, an ORC expander, an alternator, a heat recuperator and a condenser. The heat of biomass combustion in the boiler is used to generate hot water, which is then used to heat and vaporise the organic working fluid through the evaporator. The organic fluid vapour drives the expander to rotate an alternator, producing power. The expanded organic fluid vapour leaving the expander first passes through the heat recuperator and then is condensed in the condenser. The cooling water leaving the condenser can be heated to a temperature (∼46°C) suitable for domestic washing and under-floor heating etc. Testing results of the micro-CHP system with a 50kWth biomass-pellet boiler are analysed and presented in this paper. The current micro-CHP generated 861W electricity and 47.26kWth heat, corresponding to electricity generation efficiency of 1.41% and CHP efficiency of 78.69%. Further improvements on the performance of the expander and the alternator assembly as well as the design of the biomass boiler’s heat exchanger need to be addressed in the future.

Optimal sizing of biomass-fired Organic Rankine Cycle CHP system with heat storage

A novel methodology for Optimal Sizing of Biomass-Fired Organic Rankine Cycle (ORC) Combined Heat and Power (CHP) System with Heat Storage is presented in this paper. The ORC technology received a lot of attention recently, especially for medium scale applications (e.g. district heating) where market potential is substantial. Another push for the technology is provided in the context of recent EU regulations to tackle the rising environmental problems, i.e. the 20-20-20 directive, which should provide another boost for the use of renewables in electric power systems. In this study, the simulation of the operation of a biomass-fired ORC CHP system is discussed first, where the dispatch of the plant is optimized to maximize the profits from electricity and heat sales. Based on the optimal dispatch values, an economic evaluation is carried out to determine the feasibility of the proposed scheme for investment purposes; this evaluation is based on calculations of modified internal rates of return for a realistic scenario. Lastly, an optimization procedure for optimal sizing of the generation architecture is convolved with the optimal operation and economic evaluation models, to achieve maximal rates of return on the ORC CHP investment. The results of the present studies demonstrate that the heat storage is not economically feasible in the assumed setup making profits from increasing the flexibility of the ORC CHP operation. Furthermore, the results show favorable economic parameters for the ORC CHP setup without the heat storage for annual heat demands higher than 5 GWh and biomass prices lower than 17 EUR/MWh.

Preliminary experimental investigations of a biomass-fired micro-scale CHP with organic Rankine cycle

The continual increases in global energy demand and greenhouse gas emissions call for more and more utilization of sustainable energy sources such as biomass. Among the existing biomass conversion technologies such as combustion, gasification and biochemical approaches, combustion is the most mature and widely used conversion technology. Several biomass-fired combined heat and power (CHP) plants with capacities in the order of 1000 kWe have been demonstrated in several European countries. However, biomass-fuelled micro-scale CHP (1-10 kWe) suitable for domestic applications has yet to be commercialized or demonstrated. The micro-scale biomass-fired organic Rankine cycle (ORC) CHP system currently developed by the authors mainly consists of a biomass boiler, an ORC fluid evaporator, an ORC turbine, an alternator, a heat recuperator and a condenser. The boiler produces hot water which transfers heat to the organic working fluid via the evaporator. The generated organic fluid vapour drives a turbine to rotate an alternator, producing power. The expanded organic fluid vapour leaving the turbine transfers some of its heat to the recuperator and then is condensed by cooling water which can be heated to around 408C for domestic washing and under-floor heating purposes. The preliminary testing of the CHP system has been carried out initially with a 9 kW electric boiler and then with a 25 kWth biomass boiler. The experimental findings of these preliminary tests are analysed and presented in the present paper.