Combined Heat And Power Plant Research Articles

Optimal regimes of heavy oil transportation through a heated pipeline

Heavy oil with a high pour point and high viscosity is transported in a heated oil pipeline with many oil pumping and heating stations. Electricity and fuel costs account for a large share of total pumping cost. Minimizing the total operating cost of pumps and heating furnaces used to pump oil requires optimization of their hydrodynamic parameters, and, above all, the distribution of pressure and temperature along the pipeline. The application of graph theory and dynamic programming to determine the problem of the global optimum of energy consumption is given in a heated oil pipeline with many oil pumping and heating stations. The problem of mass and heat transport was solved numerically. The results of the optimization problem were applied to a digital section of a heated trunk interstate oil pipeline 450 km long. The results of thermohydraulic calculations were consistent with the actual data of the Supervisory Control and Data Acquisition (SCADA) system. Energy saving is 38.9 % in the optimal regime.

Simulation of an Integrated Anaerobic Digestion and Combined Heat and Power System for Food Waste Utilization

AbstractDemand for renewable energy such as biogas is increasing because it is considered a clean and environmentally friendly source of energy and has the potential for minimizing carbon emissions. Biogas production through anaerobic digestion (AD) of organic materials is considered one of the most sustainable ways. It can be utilized directly or indirectly to generate heat, electricity, or mechanical energy for transportation. One of the most effective ways to use biogas is the combined heat and power (CHP) system, especially in combination with simulation software to facilitate the whole process without an actual experimental setup, easing the evaluation and analysis process. This study aims to develop an integrated model of AD for biogas production from food waste and CHP plants, through simulation using Aspen Plus software. The simulated results show that the developed process model can predict the heat and power produced from food waste feedstock.

A techno-economic assessment of CO2 capture in biomass and waste-fired combined heat and power plants – A Swedish case study

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.

An Experiment with Flame Combustion of a Mixture of Brown Coals at the Zheleznogorsk Combined Heat and Power Plant (CHPP)

An Experiment with Flame Combustion of a Mixture of Brown Coals at the Zheleznogorsk Combined Heat and Power Plant (CHPP)

GIS-based evaluation of solar and biomass perspectives – Case study of China regions

The spatial distribution of biomass resources is not uniform. At present, the zoning of biomass energy development suitability is primarily based on resource potential, whereas energy demand is ignored as an important factor affecting the degree of local energy self-sufficiency. Under the constraints of high transportation costs, solar energy with low geographical constraints can be a supplementary energy source for biomass despite its instability. Based on the energy utilization potential of solar energy and biomass resources, this paper evaluates the energy surplus factor (ratio of renewable resource potential to energy demand) of each city in the study area, takes meeting the specific energy surplus factor as the construction prerequisites of biomass combined heat and power (CHP) plants, calculates the biomass resource utilization rate and energy surplus factor in the study area under different conditions, and provides zoning suggestions and data reference for the unified planning of biomass CHP plants. The minimum energy surplus factor that is suitable for the development of biomass energy is set as the construction threshold of biomass CHP plants (The construction threshold is the minimum condition for the construction of biomass CHP plants. Only areas where the energy surplus factor reaches the preset construction threshold are allowed to build biomass CHP plants). The results show that the construction threshold is negatively correlated with the utilization rate of biomass resources. When the construction threshold is less than 1.4, the utilization rate of biomass resources decreases rapidly with the increase of the construction threshold; when the construction threshold is greater than 1.4, the utilization rate of biomass resources decreases slowly and tends to be flat. It is suggested that biomass resources should be developed in different regions and in stages, and priority should be given to developing areas with an energy surplus factor greater than 1.4. Areas with an energy surplus factor of 0.3–1.4 are considered secondary development areas, and areas with an energy surplus factor of less than 0.3 are not recommended for development; these can meet 31% and 59% of the total energy demand and reduce 50319380 tons and 180524400 tons carbon emissions so that the limited construction cost can meet higher energy demand and biomass resource utilization.

Heat current method-based real-time coordination of power and heat generation of multi-CHP units with flexibility retrofits

Real-time coordination and optimization of multiple combined heat and power (CHP) units under off-design conditions benefits overall efficiency improvement, whereas the coupling of power and heat generations among multi-units makes the system more complex. The existing software cannot tackle model accuracy and prompt optimization simultaneously. Herein, a heat current method-based real-time coordination method of power and heat generation is proposed. An optimization platform consisting of four software modules and corresponding hardware is developed to search for the optimal operating state of multi-units in a CHP plant with flexibility retrofits. After system modeling based on the heat current method, the data acquisition and curation module reads data from the distributed control system (DCS) server and then the parameter identification module provides the characteristic parameters of each component for optimization. The hierarchical and categorized algorithm is applied to solve the heat current-based model of the integrated cogeneration system, and the genetic algorithm is used for optimization. The information output module displays the optimized results on the DCS client interface. The platform is deployed in a practical plant with two connected CHP units. Field test results show that the reduction of standard coal consumption of the whole plant reaches up to 3.10 g/kWh.

High-temperature thermal storage in combined heat and power plants

The combined-heat-and-power (CHP) plants play a central role in many heat-intensive energy systems, contributing for example about 10% electricity and 70% district heat in Sweden. This paper considers a proposed system integrating a high-temperature thermal storage into a biomass-fueled CHP plant. The potential and benefits for the individual CHP plant, as well as for the electric grid at large-scale implementation, are studied. The original and integrated systems have been compared by energy and exergy analysis, the results indicating only minor differences. Individual CHP companies can benefit from saving fuel and become more flexible towards customer demands. The integrated system can contribute to new storage capacity in the national electric grid, valuable as the share of variable renewable electricity increases, such as wind and solar power. In a reasonable future scenario with a broad implementation of the integrated system, 53% of electricity that would otherwise be curtailed, could be absorbed and used. At the same time it will be able to replace about 21% of the fuel in the CHP plants. This can help to phase out nuclear power towards the goal of “100% renewable electricity”.

Energy efficiency of operational regimes of combined heat and power plants of industrial enterprises

Enterprises with energy-intensive production have combined heat and power plants (CHP) in their structure. During the implementation of energy saving measures, it is possible to achieve different ratios between the indicators of the efficiency of consumption of thermal and electrical energy by enterprises for production. With certain ratios between specific heat and electricity consumption in production, the enterprise is forced to buy a certain part of the electricity in the district power system (DPS) to prevent the discharge of steam exhausted by the turbine into the atmosphere or to deliver excess electricity of its own generation to the DPS. The problem cited in the article indicates that the choice is determined by the prices for fuel for CHP and the ratio between the prices for electricity purchased in the DPS and delivered to the DPS. Although electricity consumption in the production of sugar does not exceed 11% of the energy of the fuel, it is profitable to generate it in excess (turbine generators operate at maximum, close to the nominal mode) and deliver it to the distribution zone at a price higher than the cost. The proposed method for selecting operating modes for CHP turbine plants using the example of a sugar plant, which can also be used for the construction industry, as well as a method for determining energy costs for all operating modes of a sugar plant turbine plant. The influence of the cost of electricity in the distribution zone on the choice of the mode of operation of turbine plants of the CHP, which provide the minimum financial costs for the energy supply of the enterprise, has been established. A method for determining the standard size of a CHP turbine plant that satisfies the specific indicators of heat and electricity consumption of an enterprise is presented.

Local Energy Markets in Action: Smart Integration of National Markets, Distributed Energy Resources and Incentivisation to Promote Citizen Participation

Since the Paris Agreement in 2016, the goals of limiting climate change and moving toward climate resilience stand. With a share of about 80% of global CO2 emissions, the energy sector is an essential driver for these goals. A shift to low-carbon energy production and a decentralized system for more efficient energy transmission distribution is necessary. In this paper, we present our work on Modelling of Power Exchanges, Algorithms for Local Energy Market (LEM), Competitiveness of Combined Heat and Power Plant (CHP) and Energy Feedback Devices. The study was conducted considering technical, economic, social and regulatory framework. For easy integration into energy simulations or a district energy management system (DEMS), a model for power exchanges was created that allows flexible input or deterministic price patterns. The algorithm handles the clearing of an LEM by a district aggregator using limit orders with the goal of increasing the share of locally consumed electricity using economic incentives. An investigation was conducted into the operation of flexible CHPs in low-carbon power systems to balance the volatility of renewable energy. An Energy Signal Light (ESL) was developed as an energy feedback device, which is integrated into the DEMS in a living lab and allows individual configuration. In summary, the results presented should be compared with those of other research approaches in the future and require qualitative and quantitative evaluation.

The Impact of Thermo-Modernization and Forecast Regulation on the Reduction of Thermal Energy Consumption and Reduction of Pollutant Emissions into the Atmosphere on the Example of Prefabricated Buildings

The paper presents an assessment of thermal energy consumption for heating in 10 buildings made in the OWT-67N prefabricated large-panel technology from 1983 to 1986. The work covers the years 2002–2020 in three periods: before and after thermal modernization and after the use of an innovative weather prediction heating system control in buildings. The analysis made it possible to assess the impact of carrying out a deep thermal modernization, and then installing a modern forecast regulation system in terms of reducing heat energy consumption for central heating purposes, as well as reducing greenhouse gas emissions, such as CO2, SOx, NOx, CO and benzo(a)pyrene, into the atmosphere. The implementation of deep thermal modernization in buildings allowed for savings of 19.8–35% of thermal energy consumption for heating. The use of additional regulation based on prediction saved from 4.8 to 23.5%, except for one building BU10, where there was an increase in final energy consumption by 2.1%. Replacing the weather regulation in heating stations with the forecast regulation additionally reduced the emission of pollutants by 11.1%, compared to the reduction of pollutants achieved as a result of the thermal modernization of buildings alone, amounting to an average of 29.7%.

Combined heat and power plants integrated with steam turbine renovations: Optimal dispatch for maximizing the consumption of renewable energy

Steam turbine renovations, including the high back-pressure (HBP) renovation and the low pressure turbine zero power output (LZPO) renovation, can enlarge the loads supply range of one single combined heat and power (CHP) unit. Focusing on renewable energy consumption and coal saving, the problem regarding the optimal dispatch of a case CHP plant with renovated CHP units is addressed in this study. The energy and exergy analysis models are developed to evaluate the performance of various types of CHP units. The models of the minimum power load and the coal consumption for the whole plant are established based on the unit combinations in case 1 to case 4. The adaptive mutation particle swarm optimization (AMPSO) algorithm is adopted to seek the optimal value and the corresponding loads distributions. Results show that the maximum energy efficiency of the HBP renovated unit and LZPO renovated unit are 87.1% and 88.2%. Moreover, the maximum exergy efficiency of the HBP renovated unit and LZPO renovated unit are 41.3% and 32.1%. In brief, the HBP renovated unit has higher exergy efficiency and lower energy efficiency than LPZO renovated unit. In terms of optimization methods, AMPSO has better performance than PSO in terms of convergence speed and getting rid of local optimum solutions. After reasonably redistributing the loads of the case plant integrating the HBP and LZPO renovations, approximately 0.191 billion kWh more renewable energy would be consumed, and about 0.069 million tons of coal and 0.181 million tons of CO2 emissions could be saved during the heating season. Optimization results show that the LZPO renovations are more effective in consuming renewable energy, and the HBP renovations can be considered as the preferable coal-saving option. This study provides a method for optimizing the operation of renovated CHP plants. In addition, for the un-renovated CHP plant such as case 1, the renovation patterns in case 2 to case 4 provide some reference once the steam turbine renovations to be considered.

System integration for combined heat and power (CHP) plants with post-combustion CO2 capture

Based on a typical 1000 MWe coal-fired power plant with ultra-supercritical parameters, this study proposes a new integration scheme for the combined heat and power (CHP) plant with post-combustion CO2 capture. By introducing a back-pressure heat supply (BPHS) turbine and a back-pressure CO2 capture (BPCC) turbine, the superheated degree of the extraction steam is effectively retrieved for parameter matching of CO2 capture and heat supply. With 90% CO2 capture efficiency and 785.06 MWth heat supply, the total efficiency penalty for the CHP plants with solid amine-based CO2 capture reaches 19.32%. To optimize the proposed integration scheme, over 90% of the waste heat in the CO2 capture is recovered by applying the absorption heat exchanger (AHE) to increase the heating capacity of the integrated system. Energy analysis results show that the heating capacity of the integrated system is increased by 64.18%. Exergy analysis results reveal that the exergy destruction of the CO2 capture process and the heat exchange between the primary and secondary heating networks is reduced by 40.27 MWex and 10.33 MWex. Economic analysis results show that the cost of electricity (COE) and the cost of CO2 avoided (COA) are reduced by 2.59 $/MWh and 4.19 $/t CO2.

Mapping the spatial distribution of NO<sub>2</sub> with in situ and remote sensing instruments during the Munich NO<sub>2</sub> imaging campaign

Abstract. We present results from the Munich Nitrogen dioxide (NO2) Imaging Campaign (MuNIC), where NO2 near-surface concentrations (NSCs) and vertical column densities (VCDs) were measured with stationary, mobile, and airborne in situ and remote sensing instruments in Munich, Germany. The most intensive day of the campaign was 7 July 2016, when the NO2 VCD field was mapped with the Airborne Prism Experiment (APEX) imaging spectrometer. The spatial distribution of APEX VCDs was rather smooth, with a horizontal gradient between lower values upwind and higher values downwind of the city center. The NO2 map had no pronounced source signatures except for the plumes of two combined heat and power (CHP) plants. The APEX VCDs have a fair correlation with mobile multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations from two vehicles conducted on the same afternoon (r=0.55). In contrast to the VCDs, mobile NSC measurements revealed high spatial and temporal variability along the roads, with the highest values in congested areas and tunnels. The NOx emissions of the two CHP plants were estimated from the APEX observations using a mass-balance approach. The NOx emission estimates are consistent with CO2 emissions determined from two ground-based Fourier transform infrared (FTIR) instruments operated near one CHP plant. The estimates are higher than the reported emissions but are probably overestimated because the uncertainties are large, as conditions were unstable and convective with low and highly variable wind speeds. Under such conditions, the application of mass-balance approaches is problematic because they assume steady-state conditions. We conclude that airborne imaging spectrometers are well suited for mapping the spatial distribution of NO2 VCDs over large areas. The emission plumes of point sources can be detected in the APEX observations, but accurate flow fields are essential for estimating emissions with sufficient accuracy. The application of airborne imaging spectrometers for studying NSCs is less straightforward and requires us to account for the non-trivial relationship between VCDs and NSCs.

Multi-Objective Optimal Integration of Solar Heating and Heat Storage into Existing Fossil Fuel-Based Heat and Power Production Systems

Increasing the share of Renewable energy sources in District Heating (DH) systems is of great importance to mitigate their CO2 emissions. The combined integration of Solar Thermal Collectors (STC) and Thermal Energy Storage (TES) into existing Combined Heat and Power (CHP) systems can be a very cost-effective way to do so. This paper aims at finding the optimal design of STC and TES systems integrated in existing CHP’s considering two distinct objectives: economic profitability and environmental impact. To do so, we developed a three-stage framework based on Pareto-optimal solutions generated by multi-objective optimization, a Technique for Order Preference by Similarity to Ideal Solution (TOPSIS)-entropy method to select the optimal solution, followed by the definition of final Operation strategy. We proposed relevant improvement of the state-of-the-art models used in similar analysis. We also applied the proposed methodology to the case of a representative, 12 MWth CHP plant. Our results show that, while the addition of TES or STC alone results in limited performances and/or higher costs, both the cost and the CO2 emissions can be reduced by integrating the optimal combination of STC and TES. For the selected, optimal solution, carbon emissions are reduced by 10%, while the Annual Total Cost (ATC) is reduced by 3%. It also improves the operational flexibility and the efficiency by peak load shaving, load valley filling and thus by decreasing the peak load boiler operation. Compared to the addition of STC alone, the use of TES results in an increased efficiency, from 88% to 92%. The optimal share of STC is then increased from 7% to 10%.

Data‐driven distributionally robust economic dispatch for park integrated energy systems with coordination of carbon capture and storage devices and combined heat and power plants

Park integrated energy system (PIES) can utilize multiple energy resources complementarily and promote comprehensive energy efficiency. However, the uncertainty of renewable energy generation poses significant challenges to the optimal operation of PIES. This paper proposes a data-driven distributionally robust optimization (DDRO) model for the day-ahead scheduling of PIESs with coordination of carbon capture and storage devices (CCS) and combined heat and power plants (CHP). First, a deterministic economic dispatch model of PIES was presented with the aim at minimizing the total operating costs of PIES and promoting the photovoltaic (PV) power accommodation. Then, a DDRO model was developed based on the historical data to yield the optimal solution in the worst PV output scenario, where the confidence set is established with comprehensive consideration of norm-1 and norm-inf constraints. Furthermore, an efficient solving framework was proposed for the DDRO based on the combination of the column-and-constraint generation (C&CG) algorithm and a duality-free decomposition method. Finally, case studies are carried out to demonstrate the effectiveness of the proposed model.

Life Cycle Greenhouse Gas Emissions and Water and Fossil-Fuel Consumptions for Polyethylene Furanoate and Its Coproducts from Wheat Straw

Polyethylene furanoate (PEF) is a bioplastic that can potentially replace its fossil-fuel counterpart, polyethylene terephthalate (PET), to reduce greenhouse gas (GHG) emissions. A life-cycle GHG, water, and fossil-fuel consumption analysis is conducted for a potential bioplastic alternative for a fossil-based PET resin, or PEF on a kg-resin basis. PEF is assumed to be produced from a lignocellulosic feedstock (i.e., wheat straw) via furanics conversion reactions through three different pathways. The system boundary includes cradle-to-gate processes including feedstock farming, pretreatment, hydrolysis, conversion into furanics, recovery, polymerization into PEF, and on-site combined heat and power (CHP) generation. While electricity export from the CHP plant is assumed to displace the U. S. grid electricity, other coproducts of PEF are assumed to distribute the emissions and energy burdens on a mass basis. The results showed that all three PEF routes achieved significant GHG reduction relative to its fossil-based counterpart (i.e., PET): 134, 139, and 163% reduction for routes 1, 2, and 3, respectively. While fossil-fuel consumptions for all three pathways were also significantly reduced (i.e., 79, 57, and 53% reduction for routes 1, 2, and 3), water consumptions for routes 1 and 2 were increased by 168 and 79%, respectively, while route 3 only achieved reduction (by 77%) relative to fossil-PET. Different sensitivity analyses were conducted, and the results showed that coproduct allocation methods and wheat straw management assumption were the most important. A preliminary analysis on the farmland area and cost required to reduce unit mass of GHGs using PEF to replace PET is also conducted, showing a promising result for both metrics: (i) 3 metric tons of GHGs reduced/ha for all three PEF pathways and (ii) affordable cost of GHG abatement for routes 1 and 2, while route 3 even generated profits.

A reliability assessment of the heating from a hybrid energy source based on combined heat and power and wind power plants

Nowadays, improvement in fuel economy (efficiency enhancement) and reduction in emissions are pressing issues for many energy systems. One of the most promising solutions is an integration of renewable with conventional energy sources running on fossil fuels. Hybrid energy sources have the advantages of both technologies and can significantly improve the efficiency of energy supply to consumers. At the same time, the non-stationary units operating as part of a hybrid energy source can cause problems with the energy (electrical and thermal energy) supply reliability (when analyzed and ensured). This study focuses on analysis (assessment) of reliability of heat output (supply) from a hybrid energy source based on a wind power plant (WPP) and a combined heat and power plant (CHPP) operating on fossil fuel since the CHPP operates following a thermal energy profile. The essential energy benefit of the proposed technology is the replacement of part of fossil fuel in the efficient heat and power cogeneration cycle at CHPP by energy generated from WPP. The methods proposed to solve reliability problem are based on some laws of the reliability theory, Markov random processes, the graph theory, etc. The reliability analysis also considers the change in heat loads, the heat storage effect (thermal inertia), and the random fluctuations in wind speed. The results of the case example have been analyzed, and some qualitative relationships characterizing general properties for similar objects have been obtained.

Economic and Environmental Potential of Large-Scale Renewable Synthetic Jet Fuel Production through Integration into a Biomass CHP Plant in Sweden

The potential of bio-electro-jet fuel (BEJF) production with integration into an existing biomass-based combined heat and power (CHP) facility was investigated. The BEJF is produced via Fischer–Tropsch (F–T) synthesis from biogenic CO2 and H2 obtained by water electrolysis. Techno-economic (TEA)- and life. cycle (LCA)- assessments were performed to evaluate the production cost and environmental impact of the BEJF production route. The BEJF mass fraction reached 40% of the total F–T crude produced. A reduction of 78% in heating demands was achieved through energy integration, leading to an increase in the thermal efficiency by up to 39%, based on the F–T crude. The total production cost of BEJF was in the range of EUR 1.6–2.5/liter (EUR 169–250/MWh). The GWP of the BEJF was estimated to be 19 g CO2-eq per MJ BEJF. The reduction potential in GWP in contrast to the fossil jet baseline fuel varied from 44% to more than 86%. The findings of this study underline the potential of BEJF as a resource-efficient, cost-effective, and environmentally benign alternative for the aviation sector. The outcome is expected to be applicable to different geographical locations or industrial networks when the identified influencing factors are met.

Electrification of multi-energy hubs under limited electricity supply: De-/centralized investment and operation for cost-effective greenhouse gas mitigation

• Decarbonization via electrification is effective, economic, advisable, challenging. • Limited centralized electricity alters optimal design of new de-/centralized assets. • Multi-objective MILP finds pareto-optimal V2G EVs and mix of converters, storages. • Full year hourly resolution allows for detailed grid and asset operational analysis. • Cost and emission breakdown reveal dominance of embodied emission and upfront cost. Electrification of residential's heating and private mobility is often seen as a cure-all solution to the sector's immense greenhouse gas (GHG) emission problem. However, the necessary supply of affordable, secure, and sustainable centralized electricity is commonly assumed unlimited in related planning efforts. Hence, it remains unclear how beneficial electrification is under limited supply. Therefore, we investigate how jointly planned de-/centralized asset upgrades and Vehicle-2-Home enabled electric vehicles can overcome such limitations exemplarily for five residential building types in Switzerland. Thereto, the proposed, novel optimizations of Multi-energy Systems based on the Energy Hub concept, which extend the classical decentralized Energy Hub perspective to include investments into centralized assets, simultaneously select, design, and operate such assets and vehicles to minimize lifecycle-emissions and -costs while covering thermal, electrical and mobility demands under scenarios of A) unlimited, B) three partially limited, and C) no (stand-alone) centralized electricity. The optimizations prove the centralized supply limitations to be crucial, as achievable CO 2eq mitigations halve on average from A) >60% over B) 45% to only C) 30%. Further, a substantially altered and wide mix of assets is optimal to overcome the identified sole supply bottleneck of electrical energy scarcity during winter. Transitioning from low-cost to low-emission solutions, natural gas based centralized gas turbines and decentralized combined heat and power plants (CHPPs) combined with air-source heat pumps are displaced by biogas CHPPs, ground source heat pumps and centralized photovoltaics, while local photovoltaics and Vehicle-2-Home usage are constants. Surprisingly, all partially limited scenarios including nuclear phase-out and additional cross-border electricity trade stops yield similar results, which enable emission mitigations of 50% over the non-electrified reference without additional annualized cost. Stronger emission mitigation proves prohibitively costly. Overall, considering limited supply avoids overestimation of achievable emission mitigation, underestimation of total costs as well as identification of too simplistic asset portfolios.

Research on the scheduling of unit operation mode for combined heat and power plants considering new energy consumption in heating season

China aims to peak carbon dioxide emissions before 2030 and achieve carbon neutrality before 2060. The traditional coal power plants need to reduce theirs power load as much as possible to reduce CO2 emissions and improve the consumption capacity of intermittent renewable energy. Nevertheless, in part of northern China, areas with a high proportion of combined heat and power (CHP) units in coal power, CHP units need to provide heat load during heating season so that the flexibility of power load adjustment for CHP units is restricted. The plant minimum operation mode model is proposed to excavate the plant-level lower boundary of power load. By analysing the heat-power coupling mechanism of each unit, under different unit commitments, the plant-level lower boundary of power load can be calculated through dispatch heat load reasonably. Then the scheduling scheme of optimal unit commitment for plant is obtained. The comparison of results with the actual operation of a case CHP plant shows that the consumption capacity of renewable energy can be increased by 1.92 billion kWh and the CO2 emissions of the reference plant could be reduced by 52.5% under the scheduling scheme of optimal unit commitment during the heating season. The reduction of CO2 emissions for the scheduling scheme of optimal unit commitment will remain more carbon allowance which can bring revenue from carbon trade market. The scheduling of unit operation mode provides a way of operation under the current policy and environmental background, how to depress the power load of CHP plants and reduce CO2 emissions in heating season.