Combined Heat And Power Model Research Articles

Optimal energy flow in integrated heat and electricity system considering multiple dynamics

Wide promotion of combined heat and power (CHP) units necessitates the combined operation of the power and heating system. However, the dynamics and nonlinearity in integrated heat and electricity systems (IHES) remain an obstacle to efficient and accurate analysis. To handle this issue, this paper constructs an optimal energy flow (OEF) model for the coordinated operation of the IHES considering the multiple dynamics. The dynamic heating system model is formulated as a set of nonlinear partial differential and algebraic equations (PDAE). The dynamic CHP model is formulated as a set of nonlinear differential and algebraic equations (DAEs). Then, the finite difference method (FDM) is adopted to make the dynamics tractable in the OEF. On this basis, a comprehensive OEF model for IHES is proposed. Simulations in two cases verify the effectiveness of the proposed method and highlight the significance of the dynamics in IHES.

Syngas Production and Combined Heat and Power from Scottish Agricultural Waste Gasification—A Computational Study

This paper explores the possibility of utilizing Scottish agricultural waste for sustainable energy, including combined heat and power (CHP). Challenges of using unconventional agricultural feedstocks for gasification are addressed, and the study is focused on the fundamental understanding of gasification processes as well as the design constraints of a commonly used downdraft gasifier. An integrated kinetic and CHP model is presented to address these, and the results demonstrate the optimal working parameters that maximize the production of high-quality syngas and power from the CHP engine. Based on the robust sensitivity analysis, an equivalence ratio (Φ) of 0.3–0.35 with moisture content (MC) less than 10% yields higher production of syngas, thus resulting in higher gasification efficiency. Moreover, an increase in Φ also favors the gasification temperature, which promotes tar cracking and results in lower tar content. Additionally, the gasification efficiency, design limitations, and challenges are addressed to optimize the gasifier design so that it can handle diverse feedstocks with high performance. Therefore, the findings are significant in the field of bioenergy and, in particular, help to expand the route of converting agricultural waste to energy.

District energy system modeling and optimal operation considering CHP units dynamic response to wind power ramp events

With the increase in clean energy penetration, its power curtailment during operation is made increasingly evident. In this circumstance, it is imperative to address the conflict between inflexible combined heat and power (CHP) units and variable wind and solar power. In this paper, a novel coordinated optimal operation strategy of a district energy system with CHP, wind power and energy storage is established with the following characteristics: the optimal installed capacity of electric energy storage (EES) is determined to smooth the high frequency fluctuation of wind power generation; the CHP units achieve dynamic response to wind power ramp events timely after EES smoothing; and the CHP model with start-stop and dynamic response mechanism is able to reduce the installed capacity of electric boiler (EB) significantly. One-week operation data is adopted in the case studies to increase the reliability of simulation results. The simulation results show that with EES integration, high frequency wind energy curtailment is reduced, the capability of peak regulation and power ramp of CHP units is enhanced by start-stop and the proposed dynamic response mechanism and environmentally sustainable and socially resilient cities is promoted.

Utilizing finned tube economizer for extending the thermal power rate of TEG CHP system

The thermoelectric generator (TEG) is an extremely useful device for converting thermal waste into electricity. To overcome the problem of the low conversion rate of TEGs, we present a model based on combined heat and power (CHP) production for simultaneous generation of electrical and thermal powers. This paper proposes a novel laboratory TEG based on CHP model for maximizing the possible output level of both powers by a compensating method. We applied an economizer section in the design of this model. Based on this method, the temperature gradient for the TEGs can rise as well. By connecting an economizer, the wasted heat from the TEGs can be compensated significantly in the second section (economizer part). To evaluate the functionality of the proposed set, we tested the performance of our prototype in two different modes: one with an economizer and another without that. The results obtained confirmed that the efficiency of the suggested TEG based on CHP system enhanced (up to 90%) by using an economizer.

An economic dispatch model for combined heat and power systems considering the characteristics of heat recovery steam generators

The installation of combined heat and power (CHP) units has rapidly increased due to their energy efficiency and environmental advantages. The broad application of CHP units requires the joint dispatch of power and heating systems, in which the modeling of CHP units plays a pivotal role. However, existing CHP models face the contradiction between accuracy and solvability. In this paper, we propose a novel CHP model that well balances these two issues. The heat exchange theory is employed to derive the models of HRSGs. Based on the models, an economic dispatch model for CHP systems that considers the characteristics of heat recovery steam generators (HRSGs) is formulated. A corresponding algorithm for solving the proposed model is presented as well. In case studies, the impacts of the HRSG characteristics on the CHP operation region and dispatch results are studied, and the performances of the proposed model and the conventional model are compared. The results indicate that the proposed model outperforms the conventional model in terms of the level of optimality achieved during economic dispatch, benefiting from the more accurate description of the electro-thermal coupling relationship of CHP units.

Modeling Combined Heat and Power Systems for Microgrid Applications

This paper presents the modeling of combined heat and power (CHP) systems for microgrid applications. When generating electricity, a CHP unit can recycle waste heat to supply building thermal loads to improve the overall efficiency of a traditional generation system. The ramping capability of a CHP unit makes it an ideal resource for load following and frequency regulation in microgrid operation. In this paper, a CHP model built in Simulink is developed. The CHP model includes three key components: generator, turbine, and absorption chiller. A new isochronous governor control strategy is proposed to provide zero-steady-state-error frequency regulation. The supply of building thermal loads is modeled to facilitate the calculation of the overall CHP system efficiency. The impact of ambient temperature on the maximum electrical output is considered. The developed model is implemented on OPAL-RT for testing the microgrid controller performance in a microgrid system.

Time-Domain Modeling of Grid-Connected CHP for Its Interaction With the Power Grid

This paper presents a nonlinear dynamic model of grid-connected combined heat and power (CHP) system that can effectively simulate the thermoelectric interactions and examine the impact of the CHP on the power grid. Based on the theorems of mass balance and energy balance, this paper studies and analyses the principles and dynamic characteristics of the main CHP components, including gas internal combustion engine, synchronous generator, waste heat exchanger, water storage tank, exhaust-heat boiler, and gas fired boiler. Then, the nonlinear time-domain models for each component are built against input and output parameters in order to facilitate the study of CHP operation under various conditions. Subsequently, a simulation method that can deal with the coupling of all models with different time constants is proposed. Finally, dynamic simulation analysis of the developed CHP model is carried out on the MATLAB/Simulink. Extensive demonstration results show that the developed models are accurate to represent the thermoelectric interactions in the gird-connected CHP and capture the impact of these gird-connected CHPs on the power grid. This study is particularly beneficial to the design of new control strategies for CHPs to maximise its efficiency and stability value to the grid.

The Significance of a Building’s Energy Consumption Profiles for the Optimum Sizing of a Combined Heat and Power (CHP) System—A Case Study for a Student Residence Hall

University buildings, such as student residence halls with year-round consistent energy demands, offer strong opportunities for Combined Heat and Power (CHP) systems. The economic and environmental feasibility of a CHP project is strongly linked with its optimum sizing. This study aims to undertake such an assessment for a CHP system for a student residence hall located in London, the United Kingdom (UK). The study also aims to undertake a sensitivity analysis to investigate the effect of different parameters on the project’s economics. Necessary data are collected via interviews with the University’s Energy Manager. Modeling of the CHP system is performed using the London South Bank University (LSBU, London, the UK) CHP model. Results demonstrate that optimum sizing of CHP is crucial for achieving higher economic and environmental benefits and strongly depends on the authenticity of the energy consumption data, based on which the CHP is being sized. Use of incorrect energy data could result in an undersized or oversized CHP system, where an oversized system will result in higher negative results compared to an undersized system. Finally, Monto Carlo statistical analysis shows that electricity price is the significant factor that could affect the project’s economics. With an increasing spark gap, the payback period decreases, and vice versa.

Techno, Economic and Environmental Assessment of a Combined Heat and Power (CHP) System—A Case Study for a University Campus

Universities in the United Kingdom that have installed Combined Heat and Power (CHP) technology are making good moves towards achieving their CO2 reduction targets. However, CHP may not always be an economical option for a university campus due to numerous factors. Identification of such factors is highly important before making an investment decision. A detailed technical, economic, and environmental feasibility of CHP is, therefore, indispensable. This study aims to undertake a detailed assessment of CHP for a typical university campus and attempts to highlight the significance of such factors. Necessary data and information were collected through site visits, whereas the CHP sizing was performed using the London South Bank University (LSBU) CHP model. The results suggest that there is a strong opportunity of installing a 230 kW CHP that will offset grid electricity and boilers thermal supply by 47% and 75%, respectively, and will generate financial and environmental yearly savings of £51k and 395 t/CO2, respectively. A wider spark gap decreases the payback period of the project and vice versa. The capital cost of the project could affect the project’s economics due to factors, such as unavailability of space for CHP, complex existing infrastructure, and unavailability of a gas connection.

Development of a Combined Heat and Power sizing model for higher education buildings in the United Kingdom

The four Higher Education Funding Councils in the United Kingdom want all universities to reduce CO2 emissions by 34% by 2020 compared to a 2005 base. Universities that have installed Combined Heat and Power (CHP) technology are making good moves towards achieving their CO2 reduction target. For a CHP project to be successful, a detailed technical, economic and environmental assessment is required. Generally, this assessment is carried out using a computer-based model. Currently, available CHP models have limitations in terms of flexibility, accuracy, reliability and complexity and their use could result in an undersized or oversized CHP scheme that could lead to a complete failure of the project. Therefore, there is an urgent need for a robust and user-friendly model, which integrates multiple features that are missing in the currently available models.This paper presents the development of a spreadsheet based CHP sizing model for a single or multiple university buildings. The major strengths of the model are its simplicity, flexibility of data entry, selection of multiple electrical and thermal demands, an in-built real database for a range of CHP sizes, multiple control strategies, multiple investment routes and their life cycle cash flow analysis, and the potential for detailed sensitivity analysis of payback period using the Monto Carlo Simulation technique. The model, which we call the London South Bank University (LSBU) CHP model, has been tested with three other CHP models for different control modes for the same building and the comparisons are discussed.

Optimal design and operation of CHPs and energy hub with multi objectives for a local energy system

This study presents a multi-objective optimization process to determine the optimal operations of combined heat and power (CHP) units and energy hub according to present value and carbon emissions. Mixed integer linear programming (MILP) model is applied to a local energy system including both electricity and gas to achieve multi objectives (energy costs versus carbon emissions). The optimization problem is formulated on the coupling electricity load and gas load with an energy hub and CHP model for optimal design and operation. The components of the energy hub includes solar thermal system, heat pump, battery, photovoltaics (PV), CHPs and thermal storage system. The results show a set of optimal design solutions of each component including their half-hourly operations and trade-off between them to achieve multi-objectives. The total cost including energy cost, carbon emission and investment with energy hub will be 112 million pound lower compared to that without energy hub system in a 20 year time frame.

Integrated Energy Systems for Higher Wind Penetration in China: Formulation, Implementation and Impacts

With the largest installed capacity in the world, wind power in China is experiencing a ∼20% curtailment. The inflexible combined heat and power (CHP) has been recognized as the major barrier for integrating the wind source. The approach to reconcile the conflict between inflexible CHP units and variable wind power in Chinese energy system is yet unclear. This paper explores the technical and economic feasibility of deploying the heat storage tanks and electric boilers under typical power grids and practical operational regulations. A mixed integer linear optimization model is proposed to simulate an integrated power and heating energy systems, including a CHP model capable of accounting for the commitment decisions and nonconvex energy generation constraints. The model is applied to simulate a regional energy system (Jing–Jin–Tang) covering 100-million population, with hourly resolution over a year, incorporating actual data, and operational regulations. The results project an accelerating increase in wind curtailment rate at elevated wind penetration. Investment for wind breaks even at 14% wind penetration. At such penetration, the electric boiler (with heat storage) is effective in reducing wind curtailment. The investment in electric boilers is justified on a social economic basis, but the revenues for different stakeholders are not distributed evenly.

Load forecasting and dispatch optimisation for decentralised co-generation plant with dual energy storage

Environmental concerns combined with the liberalisation of the energy markets has led to the emergence of small to medium-scale decentralised generation equipment embedded within transmission and distribution networks. Commonly, such plant is operated by small to medium private enterprises and dispatched independently from centralised resources. The liberalisation of energy markets has also brought about the rise of variable wholesale electricity markets, in the form of the spot (day-ahead) market and the balancing (intra-day) markets across the EU and beyond. As such, there is much interest in how decentralised generation equipment can be most profitably operated in this context. This paper focuses on short-term forecasting of both heat and electrical loads, along with unit commitment scheduling and economic dispatch optimisation, for a small/medium scale decentralised combined heat and power (CHP) plant. In the work presented the plant is assumed to be equipped with local heat and electricity storage and operating in the presence of fluctuating wholesale energy prices and local loads. The approach adopted builds on recent research employing Mixed Integer Linear Programming (MILP) models and non-linear boiler efficiency curves, and extends this work into a rolling horizon context. Results are presented which demonstrate the efficiency of the proposed approach and investigate the sensitivity of the results with respect to CHP model accuracy and load prediction accuracy. The results indicated that profit is much more sensitive to the accuracy of load predictions than indicated by previous work in the area. The findings also challenge those of recent work in the field, which suggest that a strategy of interacting with the spot (day-ahead) market only is the most profitable for small/medium scale decentralised energy producers. The results presented in this paper indicate that when load prediction inaccuracies are also considered in the CHP optimisation framework, a strategy interacting with both the spot (day-ahead) market and the balancing (intra-day) market is significantly more profitable than a strategy interacting with the spot market only.

How to manage co-product inputs in emergy accounting exemplified by willow production for bioenergy

Assessments of environmental performance are challenged by multifunctionality of production systems where impacts cannot be assigned to any one specific output. In the assessment method emergy accounting, all available energy used up for a process is summed up after being converted to solar equivalent Joules. In emergy accounting each output carries the resource use burden of all co-produced outputs. When comparing emergy indicators on a product-to-product basis (reference approach), products from single-output processes tend to be favoured. This constitutes a method bias. Building on emergy algebra rules, we describe approaches to calculate solar transformities when co-production is involved and give guidelines on how to compare products and systems. The approaches are exemplified in a comparison between willow biomass, fertilised with manure, and natural gas used as feedstock for combined heat and power (CHP) production. A Danish willow-based CHP model system was assessed whereas data for the fossil-based system was from literature. When compared on a product-to-product basis using the reference approach, bio-based CHP production is inferior to fossil-based CHP with respect to resource use (transformities of 2.31 E+05seJ/J and 0.88 E+05seJ/J, respectively). If the manure is considered as a waste and modelled as heat loss, the single-product transformity for biobased production is only 0.37 E+05seJ/J. When compared on a system-to-system basis, bio-based production is competitive with fossil-based production (transformities of 2.21 E+05seJ/J and 2.29 E+05seJ/J, respectively). The paper evaluates compatibility of suggested approaches with emergy theory and practices and presents a discussion of the distinction between waste and resource.

A Model of a Combined Heat and Power System for SAGD Operations

Abstract This paper presents a model of a combined heat and power system, also known as cogeneration, for the generation of electricity and steam for in situ bitumen extraction operations. The model simulates the operation of a gas turbine-electric generation system with the hot exhaust gases from the turbine being directed to a boiler for steam production. Alternately, a topping steam turbine-electric generation system with exhaust steam directed to the in situ operations is simulated. The model provides estimates of the fuel requirements and electricity generated by the combined process. It enables the investigation of the relationships between electricity generation, steam production and fuel requirements for these operations. Included is an illustrative example of the application of the model for the assessment of the economics of the steam assisted gravity drainage (SAGD) process using alternate fuels, natural gas and petroleum coke. Introduction Bitumen mining and in situ bitumen extraction operations in northern Alberta are large users of natural gas and are projected to grow substantially over the next decade. However, since the turn of the century, the North American natural gas supply-demand balance has tightened and, consequently, gas market prices have risen substantially. Moreover, western Canadian supplies of natural gas are projected to decline in the near-term. Environmental concerns regarding the use of fossil fuels, such as natural gas, have recently become more acute. Consequently, there is a need to identify alternate fuels and heat generation systems that could, if implemented, reduce the cost and environmental impact of bitumen extraction operations. The Combined Heat and Power Model (CHPM) described in this paper was developed specifically for the economic assessment of combined heat and power systems for bitumen extraction using the steam assisted gravity drainage (SAGD) process. It calculates the fuel requirement to provide heat for the SAGD operations as well as the associated electricity generated, which are required for the economic assessment. The economic analysis is performed in a separate model-the SAGD Supply Cost Model (SSCM)-which calculates the supply cost of the extracted bitumen. Description of the CHPM The CHPM simulates the operation of the steam plant of a SAGD operation, both with and without electricity generation. Gas and steam turbine options for the generation of electricity are included (See Figures 1 and 2, respectively). As shown in the figures, mass and heat energy flows of the system are outputs of the model. The principles of conservation of energy and mass are used for the calculation of the flows. Figure 1 shows that, in the case of the gas turbine option, natural gas fuel is burned in a gas turbine to produce electricity. Waste heat in the exhaust gases from the turbine is recovered in a boiler, which produces steam for the bitumen extraction process. There is a steam-water separator, which produces 100% quality steam for this process. Water from the separator is returned to the boiler.