Combined Heat And Power Units Research Articles

Optimal power flow based TU/CHP/PV/WPP coordination in view of wind speed, solar irradiance and load correlations

This paper addresses a novel probabilistic optimisation framework for handling power system uncertainties in the optimal power flow (OPF) problem that considers all the essential factors of great impact in the OPF problem. The object is to study and model the correlation and fluctuation of load demands, photovoltaic (PV) and wind power plants (WPPs) which have an important influence on transmission lines and bus voltages. Moreover, as an important tool of saving waste heat energy in the thermoelectric power plant, the power networks share of combined heat and power (CHP) has increased dramatically in the past decade. So, the probabilistic OPF (POPF) problem considering valve point effects, multi-fuel options and prohibited zones of thermal units (TUs) is firstly formulated. The PV, WPP and CHP units are also modeled. Then, a new method utilizing enhanced binary black hole (EBBH) algorithm and 2m+1 point estimated method is proposed to solve this problem and to handle the random nature of solar irradiance, wind speed and load of consumers. The correlation between input random variables is considered using a correlation matrix. Finally, numerical results are presented and considered regarding the IEEE 118-busses, including PV, WPP, CHP and TU at several busses. The simulation and comparison results obtained demonstrate the broad advantages and feasibility of the suggested framework in the presence of dependent non-Gaussian distribution of random variables.

Future power market and sustainable energy solutions – The treatment of uncertainties in the daily operation of combined heat and power plants

Abstract Intermittent renewable energy sources (RES) are increasingly used in many energy systems. The higher capacity of intermittent RES increases the importance of introducing flexible generation units into the electricity system balancing. Distributed district heating plants with combined heat and power (CHP) can provide this flexibility. However, in electricity systems with a high penetration of intermittent RES, CHP units are currently experiencing decreasing hours of operation, making it likely that existing CHP capacity will be phased out from the energy system. Furthermore, when the plants provide balancing for the electricity system, the complexity of their daily operation planning is increased. This article analyses and discusses how these units can improve their economic feasibility by providing balancing services to the electricity system, benefitting both each individual plant and the system as a whole. This is done by using the case of the Danish district heating plant, Ringkobing District Heating, which has a relatively high capacity of solar heating installed and is located in an area with a high penetration of wind power. It is found that the plant can increase the economic feasibility of the CHP unit by participating in the electricity balancing tasks; however, it is uncertain whether the benefits are substantial enough to keep the distributed CHP capacity in operation.

Decentralised combined heat and power in the German Ruhr Valley; assessment of factors blocking uptake and integration

Abstract Background In Germany, the energy system is undergoing reorganisation from a centralised system based on fossil fuels and nuclear power to a sustainable system based on decentralised production and consumption of energy, the so-called Energiewende. Recently, there has been more attention to improving energy efficiency in those regions where conventional energy production activities and energy-intensive industries are located, such as the Ruhr area. Although the potential for decentralised combined heat and power (CHP) units is high in this region, local action plans show only modest developments for this technology. In this paper, we address this issue by answering the following research question: Which factors block the uptake and integration of decentralised CHP in the German Ruhr area's energy system? Methods The multilevel perspective (MLP) was used to analyse the state of system innovation in relation to the uptake and integration of decentralised CHP technology. Prior to the MLP analysis, a stakeholders' analysis was conducted to identify stakeholders' views, positions and experienced barriers regarding the uptake and integration of decentralised CHP technology. Data collection included review of text documents and conducting 11 interviews. Results Due to many regime barriers blocking niche development, the uptake of decentralised CHP technology is limited. Identified barriers relate to lack of market services and mismatches with user preferences, (sectoral) policies and industrial interests. Conclusions Observed barriers relate to (i) lack of market services such as financial means for making investments; (ii) user awareness such as unawareness and information deficit regarding the benefits of decentralised CHP to potential users, (iii) the presence of centralised district heating systems, (iv) policy issues such as lack of sufficient policies supporting diffusion of decentralised CHP units, legal stipulations from social housing policies that prevent housing cooperatives from becoming energy producers and district heating systems owned by public and private owners (via concessions contracts); (v) sector issues such as lack of skilled service-providing companies; and (vi) industrial interested such as the vested interests of the coal and gas industry. Moreover, many of the mentioned barriers seem interrelated, especially those concerning policy and finance available for making upfront investments.

Stochastic Multicriteria Acceptability Analysis for Evaluation of Combined Heat and Power Units

Combined heat and power (CHP) is a promising technology that can contribute to energy efficiency and environmental protection. More CHP-based energy systems are planned for the future. This makes the evaluation and selection of CHP systems very important. In this paper, 16 CHP units representing different technologies are taken into account for multicriteria evaluation with respect to the end users’ requirements. These CHP technologies cover a wide range of power outputs and fuel types. They are evaluated from the energy, economy and environment (3E) points of view, specifically including the criteria of efficiency, investment cost, electricity cost, heat cost, CO2 production and footprint. Uncertainties and imprecision are common both in criteria measurements and weights, therefore the stochastic multicriteria acceptability analysis (SMAA) model is used in aiding this decision making problem. These uncertainties are treated better using a probability distribution function and Monte Carlo simulation in the model. Moreover, the idea of “feasible weight space (FWS)” which represents the union of all preference information from decision makers (DMs) is proposed. A complementary judgment matrix (CJM) is introduced to determine the FWS. It can be found that the idea of FWS plus CJM is well compatible with SMAA and thus make the evaluation reliable.

Techno-economic evaluation of using biomass-fired auxiliary units for supplying energy requirements of CO2 capture in coal-fired power plants

Parasitically providing the energy required for CO2 capture from retrofitted coal power plants can lead to a significant loss in output of electricity. In this study, different configurations of auxiliary units are investigated to partially or totally meet the energy requirements for MEA post-combustion capture in a 500MW sub-critical coal-fired plant. The auxiliary unit is either a boiler, providing only the heat required for solvent regeneration in the capture process or a combined heat and power (CHP) unit, providing both heat and electricity. Using biomass in auxiliary units, the grid loss is reduced without increasing fossil fuel consumption. The results show that using a biomass CHP unit is more favourable than using a biomass boiler both in terms of CO2 emission reductions and power plant economic viability. By using an auxiliary biomass CHP unit, both the emission intensity and the cost of electricity would be marginally lower than for a coal plant with capture. Further emission reductions occur if CO2 is captured both from the coal plant and the auxiliary biomass CHP, resulting in negative emissions. However, high incentive schemes (a carbon price higher than 55 $/t CO2 or a combination of lower carbon price and renewable energy certificates) or a low biomass price (lower than 1 $/GJ) are required to make CO2 capture from both the coal plant and the auxiliary biomass CHP unit economically attractive. All cost comparisons are for CO2 capture only and CO2 transport and storage are not included in this study.

Multi criteria dynamic design optimization of a small scale distributed energy system

The aim of this paper is to analyze the mutual interdependencies and trade-offs between heat storage and district heating network considering economic and ecological aspects. Therefore, a MILP (mixed integer linear programming) problem of a distributed energy system is formulated with a weighted multi-criteria objective function including profit and operational CO2 emissions. The considered components include CHP (combined heat and power) units of three different types, a thermal storage facility, a boiler, and district heating pipelines. In a single optimization step placement, quantity and capacity of all components as well as their operation is determined. The computed designs as well as the operation of the energy system are compared under varying weightings and different technology scenarios. We also conduct a sensitivity analysis of the investment costs associated with heat storage and of the piping costs for the district heating network. The results favor the construction of heat storage devices over a district heating network. This applies to both environmental impact and cost of energy supply and can be well explained by the decoupling of heat demand and electricity production, which is shown in a correlation analysis.

Small-scale combined heat and power as a balancing reserve for wind – The case of participation in the German secondary control reserve

Increasing amounts of intermittent renewable energy sources (RES) are being integrated into energy systems worldwide. Due to the nature of these sources, they are found to increase the importance of mechanisms for balancing the electricity system. Small-scale combined heat and power (CHP) plants based on gas have proven their ability to participate in the electricity system balancing, and can hence be used to facilitate an integration of intermittent RES into electricity systems. Within the EU electricity system, balancing reserves have to be procured on a market basis. This paper investigates the ability and challenges of a small-scale CHP plant based on natural gas to participate in the German balancing reserve for secondary control. It is found that CHP plants have to account for more potential losses than traditional power plants. However, it is also found that the effect of these losses can be reduced by increasing the flexibility of the CHP unit.

Short-term scheduling of combined heat and power generation units in the presence of demand response programs

This paper presents the short-term hourly scheduling of industrial and commercial customers with cogeneration facilities, conventional power units, and heat-only units. In order to serve the power and heat demands of the customer with minimum cost, demand response (DR) program has been implemented. In the proposed DR program total power and heat demand of customer will be supplied, without any curtailed load. Moreover, the responsive load can vary in different time intervals. In the paper, the heat-power dual dependency characteristic in different types of CHP (combined heat and power generation) units is taken into account and all technical constraints of generation units have been satisfied. In addition, a heat buffer tank, with the ability of heat storage, has been incorporated in the proposed framework. This work studies four cases in order to confirm the performance of the proposed method. The importance of applying the proposed DR program, the effect of considering the amount of transferable power constraint and the effect of heat exchange with the nearby factories in the value of expected profit have been investigated in the case studies.

Application of environmental performance assessment of CHP systems with local and global approaches

This paper is focused on methods to indicate the environmental impact in terms of air pollutants of CHP (Combined Heat and Power) systems. The aim is to combine the energy saving achievement with information concerning the environmental benefit, in comparison with the non-CHP scenario.Environmental impact of CHP production both on global and local scale should be taken into account. In particular, the method of the “Avoided Heat Generator” is highlighted in this study as a proper approach for CHP and is used for a local-scale environmental impact evaluation. This approach calculates the reduction of emission due to CHP operation, taking into account the amount of pollutant emitted by an equivalent heat generator, which provides the same thermal power of the CHP prime mover. Moreover, the recommended approach is compared in the paper with another proposed method, based on the PSI (Pollutant Saving Index) value, which is suitable to estimate the global-scale environmental impact.Numerical evaluations of the CHP environmental benefits, in terms of NOx, CO and CO2 emissions, are shown for several CHP systems with different technologies and electric power sizes, in order to provide a comprehensive overview of current CHP prime mover environmental performance and to serve as an application reference example of the two methods potential use, in the framework of the CHP units authorization procedure. The significant effect of the reference comparative scenario is also highlighted.

Thermodynamic, ecological and economic aspects of the use of the gas turbine for heat supply to the stripping process in a supercritical CHP plant integrated with a carbon capture installation

This paper presents the results of thermodynamic and economic analyses for eight variants of a combined heat and power (CHP) plant fuelled with coal working under supercritical steam parameters and integrated with a CO2 capture installation and a gas turbine system. The motivation behind using a gas turbine in the system was to generate steam to supply heat for the stripping process that occurs in the separation installation to regenerate the sorbent. Additional analyses were conducted for the reference case, a CHP unit in which the CO2 separation process was not conducted, to enable an economic evaluation of the integration of a CHP unit with a CO2 separation installation according to the variants proposed. The break-even price of electricity and avoided emission costs were used to evaluate the respective solutions. In this paper, the results of the sensitivity analysis of the economic evaluation indicators in terms of the change in the annual operation time, price of emission allowance and heat demand rate for the realization of the stripping process for all cases are presented.

Exergy analysis of a combined heat and power plant with integrated lignocellulosic ethanol production

Lignocellulosic ethanol production is often assumed integrated in polygeneration systems because of its energy intensive nature. The objective of this study is to investigate potential irreversibilities from such integration, and what impact it has on the efficiency of the integrated ethanol production. An exergy analysis is carried out for a modelled polygeneration system in which lignocellulosic ethanol production based on hydrothermal pretreatment is integrated in an existing combined heat and power (CHP) plant. The ethanol facility is driven by steam extracted from the CHP unit when feasible, and a gas boiler is used as back-up when integration is not possible. The system was evaluated according to six operation points that alternate on the following three different operation parameters: Load in the CHP unit, integrated versus separate operation, and inclusion of district heating production in the ethanol facility. The calculated standard exergy efficiency of the ethanol facility varied from 0.564 to 0.855, of which the highest was obtained for integrated operation at reduced CHP load and full district heating production in the ethanol facility, and the lowest for separate operation with zero district heating production in the ethanol facility. The results suggest that the efficiency of integrating lignocellulosic ethanol production in CHP plants is highly dependent on operation, and it is therefore suggested that the expected operation pattern of such polygeneration system is taken into account when evaluating the potential of the ethanol production.

Analysis on Thermal Economy and Peak-Shaving Capability for Combined Heat and Power (CHP) Unit in Varying Operating Conditions

Based on the principle of featured through-current area being constant, calculation model for parameters of regenerative steam extraction of CHP unit in different heating conditions is developed in this paper through using FROTRAN software. The generated output and thermal economy of the CHP unit are calculated by using the method of equivalent enthalpy drop, and the accuracy of the model is verified. With the purpose to analyze the rationality of different calculation methods, the distribution ratio of coal consumption for heat supply and coal consumption rate for power generation are calculated through method of equivalent enthalpy drop, heat quantity method and method of actual enthalpy drop under the same operating condition. Moreover, according to the operation test on the unit, the highest and lowest generated output of the CHP under various loads of heat supply are determined, which will provide a basis to the subsequent thermoelectric units in participating in peak shaving of power grid.

A powerful visualization technique for electricity supply and demand at industrial sites with combined heat and power and wind generation

The combination of wind generation and combined heat and power (CHP) on an industrial site brings significant design and operational challenges. The stochastic nature of wind power affects the flows of electricity imported and exported to and from the site. Economies of scale favor larger wind turbines, but at the same time it is also desirable to minimize the amount of electricity exported from the site to avoid incurring increased network infrastructure usage charges. Therefore the optimum situation is to maximize the proportion of the site load served by on-site generation. This paper looks at a visualization technique for power flows on an industrial site, which can be used to size on-site generators. The technique is applied to a test case, demonstrating how a simple combined heat and power control scheme can support the integration of on-site wind power. The addition of such CHP control has a small impact on the CHP unit but can greatly increase the proportion of wind generation consumed on-site. This visualization technique allows the comparison of different generation mixes and control schemes in order to arrive at the optimal mix from a technical and economic viewpoint.

Combined Analysis of Electricity and Heat Networks

The use of Combined Heat and Power (CHP) units, heat pumps and electric boilers increases the linkages between electricity and heat networks. Two combined analysis methods were developed to investigate the performance of electricity and heat networks as an integrated whole. These methods were based on models of electrical power flow and hydraulic and thermal circuits together with their coupling components, focusing on CHP units and circulation pumps. These two methods were the decomposed and integrated electrical-hydraulic-thermal calculation techniques in the forms of power flow and simple optimal dispatch. The comparison showed that the integrated method requires fewer iterations than the decomposed method. A case study of Barry Island electricity and district heating networks was conducted, showing how both electrical and heat demand in a self-sufficient system (no interconnection with external systems) were met using CHP units.

Economic Analysis of a Micro Humid Air Turbine for Domestic Applications

Micro Gas Turbines (mGT) appear as a promising technology for small-scale (up to 500kW) Combined Heat and Power (CHP) production. However, their rather low electric efficiency limits their profitability when the heat demand decreases. Hot liquid water injection in mGTs –particularly within the micro Humid Air Turbine (mHAT) cycle– allows increasing electric efficiency by making use of the flue gas residual heat in moments of low heat demand.Based on simulations performed on a Turbec T100 mGT –modified to operate as an mHAT– installed at the VUB, this paper presents an analysis of the economic profitability of such facility running on real network conditions. The study is performed assuming typical electricity and heat demand profiles for a domestic consumer. 25 natural gas and electricity price combinations have been taken into consideration, along with two types of domestic customers –with higher and lower heat demands. Results show that the profitability of the mHAT with respect to the equivalent CHP facility increases with higher electricity and lower natural gas prices. In particular, given a certain number of CHP running hours and a natural gas price, there is a threshold for the electricity price above which the net income of the mHAT unit is always higher than that of the corresponding CHP unit. In addition, water-cleaning costs for the mHAT case appear to constitute only 1 to 2.5% of total running costs.

Transient Stability Improvement for Combined Heat and Power System Using Load Shedding

The purpose of the paper is to analyze and improve the transient stability of an industrial combined heat and power (CHP) system in a high-tech science park in Taiwan. The CHP system installed two 161 kV/161 kV high-impendence transformers to connect with Taipower System (TPS) for both decreasing the short-circuit fault current and increasing the fault critical clearing time. The transient stabilities of three types of operation modes in CHP units, 3G1S, 2G1S, and 1G1S, are analyzed. Under the 3G1S operation mode, the system frequency is immediately restored to 60 Hz after tie line tripping with the TPS. Under the 1G1S and 2G1S operation modes, the system frequencies will continuously decrease and eventually become unstable. A novel transient stability improvement approach using load shedding technique based on the change in frequency is proposed to improve the transient stability.

Efficient Heat Generation for Resorts

This study compares the energy efficiency of two processes covering the thermal energy demand of a swimming pool: a combined heat and power (CHP) unit on the one hand, and a heat pump with internal combustion engine on the other hand. The thermal energy demand of the swimming pool was 1438 kWh per day (78% heating the pool and 22% providing hot water for showers), owing to temperate climate in the city of Toluca in central Mexico; a mean annual temperature of 13.5°C (10.5°C in January and 15.7°C in June) offers a large potential of renewable thermal energy stored in the atmosphere. Its utilization in heat pumps driven by thermal combustion engines can provide energy below 60°C; this temperature level provides hot water for showers while a lower temperature level of about 40°C heats up the pool water and swimming hall. Depending on outdoor temperature, which defines the load for the units, the efficiency in terms of total primary energy consumption is better for the CHP solution (100% and 80% load) and is better for the heat pump in the case of a 57% load. The energy losses for the CHP unit on-site are equivalent to half the losses caused by extraction and distribution of natural gas under current circumstances in Mexico. The results provide a decision tool.

A simple sizing method for combined heat and power units

We report a LDC (load duration curve) method to determine the optimum size of CHP (combined heat and power) units. The method gives the appropriate capacity graphically from the LDC of a building's heating demand. The method can be applied to the most common CHP units that are connected to the electrical grid, installed with thermal storage and auxiliary heat sources, and operated by a traditional heat-led strategy. The LDC method is simple and requires less information than existing sizing methods. Our method is in agreement with existing methods within 2.7–12.6% for internal combustion engine-driven CHP units, and 17.1–32.1% for Stirling engine-driven CHP units.

Development of a micro-cogeneration laboratory and testing of a natural gas CHP unit based on PEM fuel cells

This work discusses the design and the development of a Laboratory of Micro-Cogeneration (LMC) at Politecnico di Milano. The LMC laboratory is a unique structure devoted to small-scale power generation, with the main goals of testing and improving the performance of systems that produce or utilize electric and thermal (hot and/or cold) power in a very general sense, spanning from combined heat and power (CHP) units to heaters, from absorption chillers to heat pumps, but also able to perform tests on fuel processors and electrolyzers. The laboratory features a supply of natural gas as well as H2 and O2 from a high pressure electrolyzer and of CO, CO2 and N2 from bottles, permitting to carry out experiments with simulated synthesis fuels. The maximum allowable electrical power produced, exported to the grid or to an electronic loadbank, or consumed by the system under test is 100 kW; maximum allowable thermal power is roughly 200 kW with variable temperature water circuits (from chilled water up to a 150 °C at 8 bar superheated water loop). This work outlines also the instruments used for on-line recording of thermodynamic properties, emissions and power, aiming at monitoring and reconstructing mass and energy balances.One of the first experimental campaign has been carried out on a CHP system based on polymer electrolyte membrane fuel cells (PEM), a promising candidate for distributed CHP thanks to low pollutant emissions and good efficiency, rapid startup and flexibility, although affected by a rather complex fuel processing section to provide the appropriate fuel to the PEM. This work presents the experimental analysis of a 20 kW prototype PEM CHP system complete of natural gas processor. The prototype is operated at LMC to characterize the processing section and the thermodynamic performances of the overall system. Despite its non-optimized layout, the unit has shown encouraging total efficiency (76%) and primary energy saving index (6%).

Optimal control of combined heat and power units under varying thermal loads

This paper describes a model based optimizer that allows a combined heat and power (CHP) unit to supply backup power to a Smart Grid on the one hand and minimize the cost for heat and power supply on the other hand. The model of the CHP unit is lean but nevertheless accurately represents the unit behavior, including thermal behavior of the storage as well as the aging effect of engine starts. Thanks to the small model dimension we can solve the optimal dispatch problem efficiently using dynamic programming. Two selected soft- and hard-ware in the loop tests are discussed to demonstrate the performance of the approach. A re-optimization strategy is discussed that allows reactions to wrong predictions of external influences like weather.