A two-layer optimization framework for combined heat and power with an enhanced organic rankine cycle

With the rise of energy needs and decentralization of power generation, and especially the need for energy production from renewable sources, the use of power plants based on organic Rankine cycle is becoming more and more significant. However, this type of power plant wastes a lot of available heat after preheating of the working fluid. Combined heat and power (CHP) production enables mitigating wasted heat potential and increasing the overall efficiency of the organic Rankine cycle-based power plant. The aim of this work is thermodynamic characteristics determination and their comparison, for two organic Rankine cycle configurations for combined heat and power: split flow simple organic Rankine cycle (SF SORC) and double stage organic Rankine cycle (DS ORC). Considered geothermal sources are low to medium temperature sources between 120°C and 180°C. The methodology includes thermodynamic analysis and optimization of the specified organic Rankine cycle configurations for heat and power production from geothermal sources. The obtained results show that the combined heat and power split flow simple organic Rankine cycle (CHP SF SORC) configuration is superior to the combined heat and power double stage organic Rankine cycle (CHP DS ORC) configuration, where plant (system) efficiency can be increased up to 28% for low temperature district heating, and for district heating plant (system) efficiency usually increases from about 12% to 18% depending on the working fluid and the temperature of the geothermal fluid. With regard to combined heat and power double stage organic Rankine cycle (CHP DS ORC) configuration plant (system) efficiency can be increased up to 18% for low temperature district heating, and for district heating plant (system) efficiency usually increases from 5% to 8%.

This paper proposes a comparative performance analysis based on 4-E (Energy, Exergy, Environment, and Economic) of a bottoming pure Ammonia (NH3) based Organic Rankine Cycle (ORC) and Ammonia-water (NH3-H2O) based Kalina Cycle System 11(KCS 11) for additional power generation through condenser waste heat recovery integrated with a conventional 500MWe Subcritical coal-fired thermal power plant. A typical high-ash Indian coal is used for the analysis. The flow-sheet computer programme ‘Cycle Tempo’ is used to simulate both the cycles for thermodynamic performance analysis at different plant operating conditions. Thermodynamic analysis is done by varying different NH3 mass fraction in KCS11 and at different turbine inlet pressure in both ORC and KCS11. Results show that the optimum operating pressure of ORC and KCS11 with NH3 mass fraction of 0.90 are about 15 bar and 11.70 bar, respectively and more than 14 bar of operating pressure, the plant performance of ORC integrated power plant is higher than the KCS11 integrated power plant and the result is observed reverse below this pressure. The energy and exergy efficiencies of ORC cycle are higher than the KCS11 by about 0.903 % point and 16.605 % points, respectively under similar saturation vapour temperature at turbine inlet for both the cycles. Similarly, plant energy and exergy efficiencies of ORC based combined cycle power plant are increased by 0.460 % point and 0.420 % point, respectively over KCS11 based combined cycle power plant. Moreover, the reduction of CO2 emission in ORC based combined cycle is about 3.23 t/hr which is about 1.5 times higher than the KCS11 based combined cycle power plant. Exergy destruction of the evaporator in ORC decreases with increase in operating pressure due to decrease in temperature difference of heat exchanging fluids. Exergy destruction rate in the evaporator of ORC is higher than KCS11 when the operating pressure of ORC reduces below 14 bar. This happens due to variable boiling temperature of NH3-H2O binary mixture in KCS11 and resulting in less irreversibility during the process of heat transfer. Levelized Cost of Electricity (LCoE) generation and the cost of implementation of ORC integrated power plant is about Rs.1.767/- per kWh and Rs. 2.187/- per kg of fuel saved, respectively whereas, the LCoE for KCS11 based combined power plant is slightly less than the ORC based combined cycle power plant and estimated as about Rs.1.734 /- per kWh. The cost of implementation of KCS11 based combined cycle power plant is about Rs. 0.332/- per kg of fuel saved. Though the energy and exergy efficiencies of ORC is better than KCS11 but considering the huge investment for developing the combined cycle power plant based on ORC in comparison with KCS11 below the operating pressure of 14 bar, KCS11 is superior than NH3 based ORC.

Organic Rankine cycle (ORC) engines are suitable for heat recovery from internal combustion engines (ICE) for the purpose of secondary power generation in combined heat and power (CHP) systems. However, trade-offs must be considered between ICE and ORC engine performance in such integrated solutions. The ICE design and operational characteristics influence its own performance, along with the exhaust-gas conditions available as heat source to the ORC engine, impacting ORC design and performance, while the heat-recovery heat exchanger (ORC evaporator) will affect the ICE operation. In this paper, an integrated ICE-ORC CHP whole-system optimisation framework is presented. This differs from other efforts in that we develop and apply a fully-integrated ICE-ORC CHP optimisation framework, considering the design and operation of both the ICE and ORC engines simultaneously within the combined system, to optimise the overall system performance. A dynamic ICE model is developed and validated, along with a steady-state model of subcritical recuperative ORC engines. Both naturally aspirated and turbocharged ICEs are considered, of two different sizes/capacities. Nine substances (covering low-GWP refrigerants and hydrocarbons) are investigated as potential ORC working fluids. The integrated ICE-ORC CHP system is optimised for either maximum total power output, or minimum fuel consumption. Results highlight that by optimising the complete integrated ICE-ORC CHP system simultaneously, the total power output increases by up to 30% in comparison to a nominal system design. In the integrated CHP system, the ICE power output is slightly lower than that obtained for optimal standalone ICE application, as the exhaust-gas temperature increases to promote the bottoming ORC engine performance, whose power increases by 7%. The ORC power output achieved accounts for up to 15% of the total power generated by the integrated system, increasing the system efficiency by up to 11%. When only power optimisation is performed, the specific fuel consumption increases, highlighting that high-power output comes at the cost of higher fuel consumption. In contrast, when specific fuel consumption is used as the objective function (minimised), fuel consumption drops by up to 17%, thereby significantly reducing the operating fuel costs. This study proves that by taking a holistic approach to whole-system ICE-ORC CHP design and operation optimisation, more power can be generated efficiently, with a lower fuel consumption. The findings are relevant to ICE and ORC manufacturers, integrators and installers, since it informs component design, system integration and operation decisions.

Novel combined desalination, heating and power system: Energy, exergy, economic and environmental assessments

Chance-constrained energy and multi-type reserves scheduling exploiting flexibility from combined power and heat units and heat pumps

Environmental sustainability of integrating the organic Rankin cycle with anaerobic digestion and combined heat and power generation

With the progress of technologies, engineers try to evaluate new and applicable ways to get high possible amount of energy from renewable resources, especially in geothermal power plants. One of the newest techniques is combining different types of geothermal cycles to decrease wastage of the energy. In the present article, thermodynamic optimization of different flash-binary geothermal power plants is studied to get maximum efficiency. The cycles studied in this paper are single and double flash-binary geothermal power plants of basic Organic Rankine Cycle (ORC), regenerative ORC and ORC with an Internal Heat Exchanger (IHE). The main gain due to using various types of ORC cycles is to determine the best and efficient type of the Rankine cycle for combined flash-binary geothermal power plants. Furthermore, in binary cycles choosing the best and practical working fluid is an important factor. Hence three different types of working fluids have been used to find the best one that gives maximum thermal and exergy efficiency of combined flash-binary geothermal power plants. According to results, the maximum thermal and exergy efficiencies both achieved in ORC with an IHE and the effective working fluid is R123.

A novel combined power and heat generation system was investigated in this study. This system consists of a low-temperature geothermally-powered organic Rankine cycle (ORC) subsystem, an intermediate heat exchanger and a commercial R134a-based heat pump subsystem. The advantages of the novel combined power and heat generation system are free of using additional cooling water circling system for the power generation subsystem as well as maximizing the use of thermal energy in the low-temperature geothermal source. The main purpose is to identify suitable working fluids (wet, isentropic and dry fluids) which may yield high PPR (the ratio of power produced by the power generation subsystem to power consumed by the heat pump subsystem) value and QQR (the ratio of heat supplied to the user to heat produced by the geothermal source) value. Parameters under investigation were evaporating temperature, PPR value and QQR value. Results indicate that there exits an optimum evaporating temperature to maximize the PPR value and minimize the QQR value at the same time for individual fluid. And dry fluids show higher PPR values but lower QQR values. NH3 and R152a outstand among wet fluids. R134a outstands among isentropic fluids. R236ea, R245ca, R245fa, R600 and R600a outstand among dry fluids. R236ea shows the highest PPR value among the recommended fluids.

Thermodynamic, exergoeconomic and multi-objective optimization analysis of new ORC and heat pump system for waste heat recovery in waste-to-energy combined heat and power plant

This study evaluates the exergetic performance of a novel combined thermoelectric generator (TEG), an organic Rankine cycle (ORC), and an absorption refrigeration cycle (ARC) run by engine exhaust heat. Further, this study investigates the effect of TEG columns on system performance and provides complete information lacking in previous studies related to engine exhaust-driven TEG-ORC systems. It was found that the net TEG and ORC power increases with the number of TEG columns while the ARC’s cold energy decreases. The organic fluid flow rate requires adjustment with the number of TEG columns to heat it up to the saturation temperature at the TEG outlet. Considering R123, R245ca, and R245fa as working fluids in the ORC, R123 and R245ca are found superior to R245fa. From parametric variation, it was found that the TEG and net ORC power decrease as ORC evaporation pressure increases for both R123 and R245ca, though R245ca performs better at lower pressures, while R123 excels at higher pressures. Meanwhile, ARC’s cooling output increases with evaporation pressure, with R123 consistently providing more cooling energy than R245ca. The cooling output surpasses the combined TEG and net ORC power, especially for R123. Consequently, the total energy output increases with evaporation pressure, with R123 outperforming R245ca in all conditions. The overall system energy and exergy efficiencies for R123 were 49.97% and 40.83% with 5 columns and 10 rows of TEG modules at the recommended ORC evaporation pressure of 32 bar.

The Organic Rankine Cycle (ORC) technology is an efficient way for small-scale generation. It offers great benefits from low temperature heat sources, recovering waste heat and revaluing renewable thermal energy. This paper presents the use of ORC for power and combined heat and power generation from low temperature heat sources. Specifically, two recent applications successfully implemented in Spain are reported, based on Rank® technology: a micro generation for waste heat recovery in a ceramic industry using HT-20 kWe and a micro combined heat and power generation using solar heat with HT-C 5 kWe. Experimental data have been evaluated to check economical and technical ORC feasibility. From waste heat recovery, now up to 23 kWe are generated, 336 MWt of primary energy are saved and 44 tonnes of CO2 emissions are avoided, with a suitable payback lower than 5 years. From renewable thermal energy, now 37 MWt of primary energy are saved, 5 tonnes of CO2 emissions are avoided with a payback lower than 8 years.

Combined heat and power: save on energy spend on treatment

The effect of smart transformers on the optimal management of a microgrid

Techno-economic performance comparison of enhanced geothermal system with typical cycle configurations for combined heating and power

A low-carbon economic optimization dispatch model of integrated energy system is proposed to improve the low-carbon and economic efficiency of the integrated energy systems. Firstly, the waste heat generator with the organic Rankine cycle is introduced into the combined heat and power to decouple the combined heat and power operation, and a coupled model with an organic Rankine cycle, power to gas, combined heat and power and carbon capture system is established. Then, the ladder-type carbon trading mechanism is introduced to improve the low-carbon model. Finally, the function is established to minimize the sum of energy purchase costs, operation and maintenance costs, and environmental costs. The proposed integrated energy systems’ low-carbon economic dispatch model reduces the total operating cost by 18.9% and the carbon emissions by 83.7% by setting up different models for comparative analysis.