Allocation of GHG emissions in combined heat and power systems: a new proposal for considering inefficiencies of the system

Taking sample processes from the combined heat and power plant in Busan Fashion Color Industry Complex, the characteristics and amounts of greenhouse gas (GHGs) emissions were analysed and calculated, respectively. Based on the results, environmental assessment was evaluated for recent 3 years. The amounts of GHG emissions from 2011 to 2013 were estimated at 182,750, 184,384 and 190,250 Ton.CO2eq/year, respectively. GHG emissions from stationary combustion sources were found to be more than 99 % of the total emissions. Also, the overall eco-efficiency indicator for environmental assessment was more than 1, suggesting that these results would be beneficial for GHG emissions allowance allocations.

As the climate change can be especially traced back to CO2-emissions, it is a worldwide aim to reduce those CO2- emissions. Therefore, it is necessary to make use of regenerative energy sources and highly efficient technologies. Besides the reduction of emissions within automotive mobility significant attention is paid to heat- and electricity generation in Germany. The reason for this is that more than half of the consumed energy in Germany is used for heat generation. Besides, large parts of the heating plants are not state-of-the-art. This shows that there is a considerable savings potential in this field. In 2007, German government decided that the percentage of combined heat and power (CHP) in electricity generation is supposed to be increased to 25 % until the year 2020. In order to reach this goal, an annual additional construction of CHP-units with a power output of 700 MW becomes necessary. A contribution to this aim can be achieved by small CHP-units, so-called combined heat and power plants. A combined heat and power plant is a unit in which a combustion engine generates electricity by means of a generator in a highly efficient manner. At the same time, the developing waste heat of the engine is used for heat generation. The joint electricity- and heat generation leads to an overall efficiency which is considerably superior to any conventional heatand electricity generation. In direct comparison, the primary energy input is up to 40% lower. Compared to a coal-fired power plant the CO2-emissions are even 60% lower in a CHP powered with natural gas. Efficient energy conversion and intelligent control technology are only exemplary requirements, which are important issues in the CHP as well as in the automotive industry and which are mastered by Volkswagen. The Volkswagen combined heat and power unit “EcoBlue 2.0” stands out for a modular and compact design, and shows many similarities to the front part of a vehicle. Power unit, generator, engine control, heat exchanger and exhaust system are only a few examples for those similarities. Additional measures, such as modified valve springs, an optimised camshaft as well as a supplementary oil tank enable a long life-time in stationary operation and generate a product which stands out in competition. Sales as well as the subsequent control of the equipment are effected by the LichtBlick AG. For this purpose, the LichtBlick AG has developed the so-called fluctuating power concept, which implies a control center which can turn the combined heat and power plants on and off at the customer by remote control. The aim is the network connection of thousands of CHPs to a virtual power plant, which is able to close the gap between power requirement and -capacity within a short time and thus is a major advantage compared to the inert large power stations. The combination of the Volkswagen “EcoBlue 2.0” and the innovative fluctuating power concept of the LichtBlick AG is a totally new business model, which enables the introduction of high quantities on the energy market and thus strongly contributes to the reduction of CO2-emissions.

A combined heat and power (CHP) system generates electricity from thermal energy and generates heat by utilizing the remaining thermal energy. The system efficiency of the cogeneration system is 75–85 %, which is very high compared to existing only power generation facilities, so it is very useful for energy conservation and environmental protection. For this reason, interest in the cogeneration system is increasing worldwide. Generally, a cogeneration plant consists of a steam turbine alone or the combined power generation of a gas turbine and a steam turbine depending on the scale. The steam turbine is divided into a back-pressure type turbine and a condensing type turbine depending on the operational methodology of the steam turbine. In both cases, the shift in the return temperature of the district heating users influences the performance of the cogeneration plant, thus affecting the power generation costs of the power plant. It is possible to accurately estimate the change in the unit cost of the power generation caused by these changes, and to inflict it on the user, thereby changing the usage pattern of the user and reducing the energy consumption accordingly. In this study, the commercial combined cycle cogeneration system using back - pressure type turbine was simulated, and the change of performance of the combined heat and power plant was analyzed while changing the user facility’s total return temperature. Based on the results of this analysis, a possible loss in the plant according to the change of return temperature was predicted. Also the effect of each user’s return temperature on the plant loss was analyzed using an actual user’s return temperature data. The economic-mechanical approach, such as this study, can alleviate dissatisfaction with the user’s charge and to consume energy in a more rational way. It eventually can play a role in reducing carbon emissions.

Due to the new carbon neutral policies, many district heating operators start operating their combined heat and power (CHP) plants using different types of biomass instead of fossil fuel. The contracts with the biomass suppliers are negotiated months in advance and involve many uncertainties from the energy producer's side. The demand for biomass is uncertain at that time, and heat demand and electricity prices vary drastically during the planning period. Furthermore, the optimal operation of combined heat and power plants has to consider the existing synergies between the power and heating systems. We propose a solution method using stochastic optimization to support the biomass supply planning for combined heat and power plants. Our two-phase approach determines mid-term decisions about biomass supply contracts as well as short-term decisions regarding the optimal production of the producer to ensure profitability and feasibility. We present results based on two realistic test cases.

Integrating fast pyrolysis into existing biomass-based combined heat and power (CHP) plants offers an innovative opportunity for plant operators to acquire an additional heat sink and produce a renewable transport fuels feedstock. This technology is particularly interesting in Sweden, where biobased heat and power constitute an important part of the energy system. It is important to establish the GHG emissions reduction of the production, through e.g. substitution effects in the transport sector, to ensure coherence with climate ambitions. In this study, the GHG emission avoidance methodology in the newly introduced EU Innovation Fund (IF) was adapted to determine whether integrating bio-oil production into an existing wood-fuelled CHP plant through fast pyrolysis would lead to a significant reduction in GHG emissions compared to the status quo. The results showed a reduction in GHG emissions of up to 0.24 MtCO2-eq per year, due mainly to the replacement of fossil fuels in the transport sector. A potential production volume in existing Swedish CHP plants was estimated to be 6.8–8.1 Mt of bio-oil annually, leading to a GHG emission avoidance of 8.6–10.3 MtCO2-eq/y, requiring a wood fuel input of 181–185 PJ/y. Sensitivity analysis indicated a significant potential for the reduction using input parameters for heating, electricity and hydrogen production whether pre-defined in the IF methodology or determined from case-specific conditions. However, the detailed results indicate that case-specific conditions should be used to reflect the fact that different European countries are at different stages in the transition to a fossil-free energy system. In conclusion, according to IF-based calculations, commercialisation of combined heat, power and bio-oil technology could lead to significant GHG emission avoidance across multiple sectors.

CCS Feasibility Improvement in Industrial and Municipal Applications by Heat Utilisation

Biomass from agriculture in small-scale combined heat and power plants – A comparative life cycle assessment

The paper analyses the economic value of using electric heat boilers and heat pumps as wind power integration measures relieving the link between the heat and power production in combined heat and power plants. Both measures have different technical and economic characteristics, making a comparison of the value of these measures relevant. A stochastic, fundamental bottom‐up model, taking the stochastic nature of wind power production explicitly into account when making dispatch decisions, is used to analyse the technical and economical performance of these measures in a North European power system covering Denmark, Finland, Germany, Norway and Sweden. Introduction of heat pumps or electric boilers is beneficial for the integration of wind power, because the curtailment of wind power production is reduced, the price of regulating power is reduced and the number of hours with very low power prices is reduced, making the wind power production more valuable. The system benefits of heat pumps and electric boilers are connected to replacing heat production on fuel oil heat boilers and combined heat and power (CHP) plants using various fuels with heat production using electricity and thereby saving fuel. The benefits of the measures depend highly on the underlying structure of heat production. The integration measures are economical, especially in systems where the marginal heat production costs before the introduction of the heat measures are high, e.g. heat production on heat boilers using fuel oil. Copyright © 2007 John Wiley & Sons, Ltd.

Reduced models of combined heat and power plants are required for different applications. Among other usages, they are implemented as mixed integer linear programs (MILP) in energy market models or price-based unit commitment problems to study the economic feasibility and optimal operation strategies of different units. Generic models are particularly useful when limited information is available for each considered plant. This paper presents a MILP modeling approach for combined heat and power (CHP) plants. The approach is based on energy and exergy balances and a few typical plant characteristics for different operating conditions. The reduction of electrical power output due to heat extraction is estimated by the transferred exergy to the district heating network. Furthermore, the accuracy, strengths and limitations of this approach are investigated for various CHP plant types with extraction condensing turbines designed for district heating systems. Therefore, detailed thermodynamic cycle simulations of CHP plants including part load operations are used to obtain the real plant operating conditions to compare them to the results of the described generic approach. The validation of the reduced, generic model shows that the accuracy mainly depends on the effectiveness of the heat extraction from the CHP plant. In addition, it can be seen that the main advantage of the presented exergy-based method is the inherent consideration of the feed flow temperature for the calculation of the power reduction due to heat extraction.

Cogeneration Cogeneration, also known as combined heat and power (CHP), describes the simultaneous production of both mechanical energy and useful heat from various sources of energy by a thermodynamic process in a technical plant [1, 2]. Combined heat and power plant (CHP Plant) A combined heat and power plant (CHP plant) or cogeneration plant provides simultaneously electricity and useful heat. Electricity generation efficiency Electricity generation efficiency or electrical efficiency is the ratio between the electricity output and the energy input of an energy conversion system.Whereas small-scale CHP plants with combustion engines feature electricity generation efficiencies of roughly 30%, large-scale CHP plants obtain up to 45% [3, 4]. Energy conversion efficiency Energy conversion efficiency or overall conversion efficiency is the ratio between the useful energy output and the energy input of an energy conversion system. For CHP plants, energy conversion efficiency is the sum of electricity conversion efficiency and heat conversion efficiency. Electrical and thermal auxiliary

• Modeling of combined heat and power (CHP) flexibility in an energy system context. • Operational flexibility is important for biomass-fired CHP plant competitiveness. • Net load volatility impacts CHP plant dispatch and use of flexibility measures. • CHP investments are sensitive to fuel cost, in competition with power-to-heat. Variable renewable electricity generation is likely to constitute a large share of future electricity systems. In such electricity systems, the cost and resource efficiency can be improved by employing strategies to manage variations. This work investigates combined heat and power (CHP) plant flexibility as a variation management strategy in an energy system context, considering the operation and cost-competitiveness of CHP plants. An energy system optimization model with detailed representation of CHP plant flexibility is applied, covering the electricity and district heating sectors in one Swedish electricity price area. The results show that investments in CHP plants are dimensioned based on the demand for district heating rather than electricity. In the system studied, this implies that CHP plant capacity is small relative to electricity system variations, and variation management using CHP plants has a weak impact on the total system cost of supplying electricity and district heating. However, flexibility measures increase CHP plant competitiveness in scenarios with low system flexibility (assuming low availability of hydropower or no thermal energy storage) although investments in CHP capacity are sensitive to fuel cost. It is found that while district heating is the dominant CHP product (constituting 50%–90% of the annual CHP energy output), the dispatchable electricity supply has a high value and comprises around 60% of the annual CHP plant revenue. In all scenarios, operational flexibility of the boiler is more valuable than a flexible steam cycle power-to-heat ratio.

The purpose of this study is to compare the effect of a reduction in greenhouse gas (GHG) emissions between the combined heat and power (CHP) plant and boiler, which became the main energy-generating facilities of “anaerobic digestion” (AD) biogas produced in Korea, and analyze the GHG emissions in a life cycle. Full-scale data from two Korean “wastewater treatment plants” (WWTPs), which operated boilers and CHP plants fueled by biogas, were used in order to estimate the reduction potential of GHG emissions based on a “life cycle assessment” (LCA) approach. The GHG emissions of biogas energy facilities were divided into pre-manufacturing stages, production stages, pretreatment stages, and combustion stages, and the GHG emissions by stages were calculated by dividing them into Scope1, Scope2, and Scope3. Based on the calculated reduction intensity, a comparison of GHG reduction effects was made by assuming a scenario in which the amount of biogas produced at domestic sewage treatment plants used for boiler heating is replaced by a CHP plant. Four different scenarios for utilizing biogas are considered based on the GHG emission potential of each utilization plant. The biggest reduction was in the scenario of using all of the biogas in CHP plants and heating the anaerobic digester through district heating. GHG emissions in a life cycle were slightly higher in boilers than in CHP plants because GHG emissions generated by pre-treatment facilities were smaller than other emissions, and lower Scope2 emissions in CHP plants were due to their own use of electricity produced. It was confirmed that the CHP plant using biogas is superior to the boiler in terms of GHG reduction in a life 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%.

The need to reduce global CO2 emissions is urgent and might be facilitated by carbon capture and storage (CCS) technologies. Sweden has a goal to reach net-zero emissions by 2045. Negative emissions and bio-CCS (BECCS) have been proposed as important strategies to reach this target at the lowest cost. The Swedish district heating sector constitutes a large potential for BECCS, with biogenic point sources of CO2 in the form of combined heat and power (CHP) plants that burn biomass residues from the forest industry. This study analyzes the potential of CO2 capture in 110 existing Swedish biomass or waste-fired CHP plants. Process models of CHP steam cycles give the impacts of absorption-based CCS on heat and electricity production, while a district heating system unit commitment model gives the impact on plant operation and the potential for CO2 capture. The results provide a cost for carbon capture and transport to the nearest harbor by truck: up to 19.3 MtCO2/year could be captured at a cost in the range of 45–125 €/tCO2, corresponding to around 40% of the total fossil fuel-based Swedish CO2 emissions. This would be sufficient to meet a proposed target of 3–10 Mt/year of BECCS by 2045.

Combined Heat and Power (CHP) plants serving Small and Medium Size Enterprises (SMEs), form the back bone of on-site generation capacity, replacing existing on-site thermal energy plant and substituting, to a large extent, the commercial electricity supply. Other benefits of CHP projects include: reduction of greenhouse gas emission, increase in SME business reliability, improved electrical power quality, increased energy efficiency, resulting in significant financial and environmental benefits. The generation and supply of electricity from power stations is generally at an efficiency in the range 25%-50% based on the Gross Calorific Value (GCV) of the fuel and including transmission and distribution losses. When employing recovery of waste exhaust heat, CHP schemes typically achieve overall efficiency of 60%-80% and sometimes more, as well as achieving a reduction in harmful gas emissions. The case study for the paper was undertaken at a large hotel. The paper discusses findings and results based on one year's data collection (2006) in order to give an insight on CHP impact on electrical and thermal energy supply as well as on the emission of greenhouse gases, particularly CO2. Also the paper gives an insight on the operational performance of the CHP plant such as: effective electrical efficiency, effective thermal efficiency, total CHP efficiency, percentage fuel savings and CO2 emission savings.