Coal-fired Combined Heat And Power Research Articles

Replacing Fossil-Fueled Combined Heat and Power Plants with Malta’s Pumped Heat Energy Storage Technology to Provide Clean Power and District Heat

This study analyzes the potential integration of a 100 MWel, 36-hour Malta Pumped Heat Energy Storage (PHES) system into the district heating network of the city of Hamburg, Germany, using energy from a nearby offshore wind farm that would otherwise be curtailed to charge the system. Publicly available data showing the times when curtailment instructions were given by the transmission system operator were used to determine the hours during which the storage system should be charged. Malta’s proprietary hourly performance model was used to simulate the behavior and performance of different plant configurations. It was shown that this configuration could avoid the curtailment of 227 GWhel of wind energy per year. The study showed that the system could provide 117 GWhel of electricity to the grid, as well as 72 GWhth of thermal energy for Hamburg’s district heating network, during periods where less renewable energy was available. This system could reduce the annual CO2 emissions by 101,400 tonnes compared to the coal-fired combined heat and power (CHP) plant that it would replace.

Integration of compressed air energy storage into combined heat and power plants: A solution to flexibility and economy

To achieve carbon neutrality, conventional coal-fired combined heat and power (CHP) plants require higher operation flexibility to improve the grid's accommodation for renewable energy. Based on the promising converging interests between compressed air energy storage (CAES) and CHP, a novel CHP-CAES system with higher operation flexibility, energy efficiency, and round-trip efficiency (RTE) is proposed in this paper. The novelty of this system is that the released compression heat of CAES during the charge process can be recovered by the CHP, and the heat consumed during the discharge of CAES comes from the primary district heating network (DHN) instead of CHP. Firstly, the theoretical feasibility of the proposed CHP-CAES system is verified. Then, the operation flexibility, energy efficiency, and RTE of the CHP-CAES system are investigated. Results show that when the output heat of the CHP-CAES system is the design value of 150 MW, the power overload capacity can be increased by 3.04 %, and the feasible minimum load is decreased by 2.00 % of the design power. The maximum energy efficiency of the CHP-CAES system is increased from 68.38 % to 69.57 %, compared with the separate CHP system. Besides, the RTE of the CAES component is increased from 64.35 % to 77.05 %. Further, optimized scheduling strategies of this CHP-CAES system are proposed for the renewables accommodation scenario. Results show that the imbalance between power provision and demand can be notably reduced from 416.68 MWh to 1.01 MWh after the integration of the CAES system. Moreover, the profitability of the CHP-CAES system also would be improved by 14,449CHY by adopting the proposed scheduling strategies on the reference day, benefiting from the time-of-use (TOU) electricity price.

Performance assessment of the novel coal-fired combined heat and power plant integrating with flexibility renovations

The operational flexibility of coal-fired combined heat and power (CHP) plants is critical for the power grid to accommodate high-penetration renewable energy. Flexibility renovations, including the high back-pressure (HBP) renovation and the low-pressure turbine zero power output (LZPO) renovation, are integrated within CHP plants and can enhance the heat-power supply flexibility. In this study, the existing two renovations are compared in consideration of flexibility, energy and exergy performance. The performance assessment of the novel CHP plant integrating with flexibility renovations are conducted. Quantitative analyses are then conducted on a characteristics day. Results show that compared with the HBP renovation, the LZPO renovation presents greater potential to improve the accommodation of renewable energy and energy efficiency, whereas is not satisfactory in larger exergy loss. Besides, compared with the conventional plant, the feasible peak-shaving capacity and heating capacity of the novel renovated plant are improved by 43 MW and 320 MW, respectively. The maximal energy utilization efficiency increases from 71.70% to 80.91%, and the exergy loss decreases from 216.9 MW to 151.2 MW. Moreover, the accommodation of renewable energy increases by 5.1 million kWh while the standard coal consumption rate for power generation decreases from 248.3 g/kWh to 222.3 g/kWh.

Integrated heat and power optimal dispatch method considering the district heating networks flow rate regulation for wind power accommodation

Wind curtailment has been severe in northeast China since the “heat-led” operation mode of the coal-fired combined heat and power (CHP) units restrains the flexibility of the power systems. District heating networks (DHN), which owns the thermal inertia, can be integrated into the power dispatch to increase the heat output of the CHP units ahead of midnights and to reduce the CHP's heat and power output at midnights, thus improving the wind power accommodation. However, almost all the integrated heat and power dispatch models ignored DHN flow rate regulation, which is a significant method to influence thermal inertia as well as the users' thermal comfort. Thus, this paper proposes a new approach to improving wind power accommodation by integrating the DHN flow rate regulation into the power dispatch. Results show that the wind power accommodation increases with the increasing flow rate due to the increasing thermal inertia. The wind power curtailment at a flow rate of 1.0 m∙s−1 decreases by 5.5% compared to that at 0.5 m∙s−1. However, the flow rate cannot be too high because fairly high electricity consumption of water pumps would become the main reason for improving wind power accommodation, which is meaningless.

Thermo‐Economic Analysis of a Plasma‐Gasification‐Based Waste‐to‐Energy System Integrated with a Supercritical CO2 Cycle and a Combined Heat and Power Plant

Herein, a novel hybrid design that combines hazardous waste plasma gasification, gas turbine, supercritical CO2 cycle, absorption heat pump, and coal‐fired combined heat and power (CHP) plant is proposed. In the integrated scheme, medical waste and concentrated solution of desulfurization wastewater are sent to the plasma gasifier and converted to syngas, which is conveyed into the gas turbine system after the necessary treatment. In terms of waste heat utilization of syngas and flue gas, some are used to drive the supercritical CO2 cycle, some are used by the absorption heat pump for heating, and the rest are used to heat the feedwater of the coal‐fired CHP plant directly. Based on a typical coal‐fired CHP plant, the benefits of this system are examined in terms of both thermodynamics and economics. Once the heat supply and the net electricity from coal remain the same, the net power generated by the waste in the hybrid design is 18.45 MW, while the net waste‐to‐electricity efficiency reaches 47.40%. In just 4.76 years, the initial investment in the proposed system is recouped, and in its 25 year lifetime, the system achieves a net present value of 150,491.81 k$.

Steam-Water Modelling and the Coal-Saving Scheduling Strategy of Combined Heat and Power Systems

China aims to peak carbon emissions by 2030. As a result, small-scale coal-fired combined heat and power (CHP) units and self-provided units are gradually shut down, and large-scale coal-fired CHP units are a solution to undertake the industrial heat loads. From the perspective of the industrial heat load allocation during the non-heating season, the problems regarding the coal-saving scheduling strategy of coal-fired CHP units are addressed. The steam-water equations of CHP units are established to analyze the heat-power coupling characteristics. The energy utilization efficiency, exergy efficiency and the coal consumption are analyzed. The optimization model of saving coal consumption is established and the adaptive mutation particle swarm optimization (AMPSO) is introduced to solve the above model. The 330 MW coal-fired CHP unit is taken as an example, and the results show that for the constant main flow rate, each increase of 1 t/h industrial steam extraction will reduce the power output by about 0.321 MW. The energy utilization efficiency and the exergy are mainly influenced by industrial steam supply and the power load, respectively. For the CHP system with two parallel CHP units, the unequal allocation of industrial heat load between two units saves more coal than equal allocation. The coal consumption can be reduced when the unit with lower power load undertakes more industrial heat load. In the typical day, the total coal consumption after optimization is 3203.92 tons, a decrease of 14.66 tons compared to the optimization before. The two CHP units in the case can benefit about 5,612,700 CHY extra in one year.

Assessing the Effects of Uncertain Energy and Carbon Prices on the Operational Patterns and Economic Results of CHP Systems

In the power and heat sectors, the uncertainty of energy and carbon prices plays a decisive role in the rationale for decommissioning/repurposing coal-fired CHP (combined heat and power) systems and on investment decisions of energy storage units. Therefore, there is a growing need for advanced methods that incorporate the stochastic disturbances of energy and carbon emission prices into the optimization process of an energy system. In this context, this paper proposes an integrated method for investigating the effects of uncertain energy and carbon prices on the operational patterns and financial results of CHP systems with thermal energy storage units. The approach combines mathematical programming and Monte Carlo simulation. The computational process generates feasible solutions for profit maximization considering the technical constraints of the CHP system and the variation of energy and carbon emission prices. Four scenarios are established to compare the operational patterns and economic performance of a CHP system in 2020 and 2030. Results show that in 2020, there is an 80% probability that the system’s annual profit will be less than or equal to €30.98 M. However, at the same probability level, the annual profit in 2030 could fall below €11.88 M. Furthermore, the scenarios indicate that the incorporation of a thermal energy storage unit leads to higher expected profits (€0.74 M in 2020 and €0.71 M in 2030). This research shows that coal-fired CHP plant operators will face costly risks and potentially greater challenges in the upcoming years with the increasing regulatory and financial pressure on CO2 emissions and the EU’s plan of phasing out fossil fuels from electricity and heat generation.

Thermo-economic comparison of heat–power decoupling technologies for combined heat and power plants when participating in a power-balancing service in an energy hub

Heat–power decoupling (HPD) technologies, which are integrated within combined heat and power (CHP) plants and can enhance the supply-side flexibility of CHP plants, have gained increased attention worldwide in recent years. This study focuses on analyzing and evaluating the effectiveness of existing HPD technologies for CHP plants in consideration of energy consumption characteristics, capital cost, and renewable power accommodation. Three categories of HPD technologies are evaluated, which are thermal energy storage, power-to-heat, and steam turbine renovation (STR). Thermo-economic models of HPD technologies and CHP plants are developed, and new performance indicators, including peaking energy saving ratio, peaking cost ratio, and minimum profitable subsidy power price, are defined. With a coal-fired CHP plant as the reference case, HPD technologies are evaluated quantitatively. Results show that the energy saving rates of HPD technologies accommodating the same amount of renewable power differ obviously, which should be considered in the design and development of HPD technologies. The economic performance of HPD technologies is mainly determined by the cost of decreased power sale and the expenditure reduction because of decreased fuel consumption. The minimum profitable subsidy power prices for thermal energy storage tank, electric boiler, heat pump, and STR are 12.7, 13.6, 11.7, and 42.0 USD⋅MWh−1, respectively. Moreover, sensitivity analysis of main parameters to the thermo-economic performance of HPD technologies is performed. The results of this study can guide the design, operation, and technological enhancement of HPD technologies.

Optimal sizing of thermal energy storage systems for CHP plants considering specific investment costs: A case study

In the next decades, energy storage technologies will play a major role in decarbonizing the European heating and cooling sector. In this regard, the deployment of complementary technologies is of paramount importance for the energy transformation of the Polish heating sector. This work addresses the challenge of sizing large-scale thermal energy storage (TES) systems for combined heat and power (CHP) plants connected to district heating networks and participating in day-ahead electricity markets. In this paper, a method based on a mixed-integer linear programming approach is proposed to find the optimal capacity of TES units connected to coal-fired CHP systems. The model considers the specific investment costs of the storage technology and optimizes the annual operation scheduling of the CHP-TES system. The model is applied to the case study of a coal-fired CHP system. Four scenarios are used to investigate the performance of the CHP system and evaluate the effects of rising carbon prices on the optimal capacity of the TES unit. The results reveal that the integration of the TES leads to a significant drop in the utilization of the heat-only boilers, helping mitigate fuel and environmental costs.

Thermodynamic optimization of coal-fired combined heat and power (CHP) systems integrated with steam ejectors to achieve heat–power decoupling

The operational flexibility of combined heat and power (CHP) units is highly required owing to the high penetration level of intermittent renewable power. Traditional CHP units should run in heat-controlled mode, which limits their operational flexibility. Therefore, the heat–power decoupling of CHP units is necessary. In this study, steam ejectors are used in designing low-cost and highly efficient heat–power decoupling systems with simple structures. Three new CHP systems integrated with ejectors are proposed, and multiple system parameters are optimized. The heat–power decoupling performances and energy consumption characteristics of the three reformed systems are also compared. Results show that all three reformed systems can achieve heat–power decoupling, and System II (coupled with two ejectors in series) has the largest peak-load regulating capacity (ΔPe) of 94.8 MW. System III (coupled with two ejectors in parallel) shows the best energy and exergy efficiencies. Compared with the Basic System, System III can enhance energy efficiency by 13.47% and the exergy efficiency by 13.46% at ΔPe of 40 MW. This study provides a promising approach for utilizing steam ejectors in enhancing flexibility for CHP plants.

Bidding Strategy of a Flexible CHP Plant for Participating in the Day-Ahead Energy and Downregulation Service Market

To integrate renewable energy generation from wind and solar radiation, most combined heat and power (CHP) plants in northern China are undergoing large-scale upgrades and retrofitting to improve operational flexibility. Simultaneously, the downregulation service (DRS) market is still retained in the day-ahead market in many provinces. Considering a flexible CHP plant with multiple types of coal-fired CHP units and heat storage as a price taker, this paper establishes a collaborative bidding strategy for the CHP plant to participate in both the day-ahead energy market and day-ahead DRS market. The bidding strategy includes the optimal output decision model, power output range model, capacity segmenting model, and bidding models for two markets determined by the marginal generation cost (MGC) and the marginal downregulation cost (MDRC), respectively. These models are validated based on realistic data from a CHP plant in Northeast China.

Operation scheduling of a coal-fired CHP station integrated with power-to-heat devices with detail CHP unit models by particle swarm optimization algorithm

The accommodation of high-penetration renewable power poses a considerable challenge to power grids. Coal-fired combined heat and power (CHP) stations are forced to enhance their operational flexibility by applying heat-power decoupling technologies. Power-to-heat devices, including electric boilers and heat pumps, are capable to enhance the operational flexibility of coal-fired CHP stations. The problem regarding the operation scheduling of a CHP station with multiple CHP units and power-to-heat devices is addressed in this study. Operation optimization models integrated with detail CHP unit models are developed, and the particle swarm optimization algorithm is utilized as the optimization algorithm. Then, a case study are carried out. Results show that the unequal distribution of heating and power loads among coal-fired CHP units can decrease the total irreversibility caused by heating steam pressure regulation. The operation scheduling method provided in this study can decrease the total coal consumption by 14.14 and 14.70 t/day for the CHP station integrated with an electric boiler and a heat pump, respectively. As a result, 1204.7 and 1252.44 ton CO2, and an additional ∼182 and ∼190 kUSD/year can be saved for the reference CHP station integrated with an electric boiler and a heat pump, respectively.

A novel cascade heating system for waste heat recovery in the combined heat and power plant integrating with the steam jet pump

Waste heat utilization is an essential approach for improving the energy utilization efficiency of the combined heat and power (CHP) plant and a significant low-carbon way to achieve clean urban heating. To recover the excess exhaust steam heat of the CHP plant with the high back-pressure turbine (CHP-HBP), this paper proposed a novel heating system integrated with the steam jet pump (SJP). The EBSILON software was applied for modeling the proposed thermal system and analyzing the thermal performance of the CHP-HBP heating system under different operating conditions. On this basis, the coupled component-system design solution was proposed by combining the 1-D mathematical design model of the SJP with the heating system performance. Compared with the conventional system, under the design condition, the exhaust steam recovery rate and the heating capacity of the novel system had a significant increment of 8.66% and 31.8 MW with the same power output. Meanwhile, the total exergy loss and standard coal consumption rate for electricity generation of the novel system reduced by 5.74 MW and 6.77 g/kWh, respectively, with about 2.32% improvement in electricity generation efficiency. The critical parametric influence analysis on the overall performance showed that the novel system has better adaptability with some fluctuations of turbine back-pressure, supply/return water temperatures, and heating load. Under off-designed conditions, the recovery rate of the exhaust steam of the novel system was 5–20% higher than that of the conventional system, and the coal consumption rate and electricity generation efficiency both performed better. In all, the proposed system provided a promising method for the effective utilization of waste heat in the field of clean heating and the energy system optimization and integration for the coal-fired CHP plants.

A regional integrated energy system with a coal-fired CHP plant, screw turbine and solar thermal utilization: Scenarios for China

Regional integrated energy system has been a suitable scheme in China to satisfy eco-industrial park’s both electric and heat needs. Combined heat and power (CHP) is an efficient technology for coal-fired plants during heating seasons. Currently, wires transport electric from CHP to destination while urban pipes network transport heat from CHP to destination, respectively. However, this might not be the case in future, when eco-industrial parks are close to plants or pipes network can’t carry enough heat. This paper presents a feasible regional integrated energy system which meets both electric and heat’s needs with steam from CHP while maintaining photothermal resources’ high percent utilization. This system includes a coal-fired CHP plant, pressure matcher, steam supply pipeline, screw turbine and solar thermal utilization part. This paper set up a model of 600 MW electric power CHP with pressure matcher and screw turbine in Ebsilon software. Then the steam supply pipeline and solar thermal utilization part were developed and analyzed based on the basic thermodynamic theories with Beijing and Huzhou’s meteorological statistics taken into consideration. Besides, the operational issues of the regional system were also listed. Meanwhile, the regional integrated energy system was obtained and a lot of characteristics were analyzed. Main devices were further investigated with energy, exergy and entransy analysis. Three extreme working situations were also carried out and discussed in the end. Several useful conclusions were drawn. It’s necessary for China to masterly integrate regional energy system with multi-energy. Moreover, pressure matcher is high-efficient in general under other parameters’ influences. This extracting steam’s technology might be considered in future. Besides, low-stent placed pipeline which can transport high-parameter steam 4 km at most was introduced. A proper mass flow value or lower inlet temperature will both reduce loss of pipeline. Furthermore, heat user side can offer electric power about 9.22 MW, heating acreage about 0.79 km2 to the eco-industrial park. More solar heat’s import, lower upper temperature difference and less sunlight will favor solar thermal utilization part. Higher heat load or lower CHP’s working condition will benefit screw turbine. Peak heat exchanger doesn’t need to work when supply domestic water temperature’s demand is less than 65 °C. The simulation in this paper might give technological statistics to the regional integrated energy system which has CHP and photothermal. This will help to put this energy system into actual use in future.

Quantitative Analysis of Energy Storage in Different Parts of Combined Heat and Power Plants

To increase the flexibility of power generation, the coal-fired combined heat and power (CHP) plants should make full use of their own energy storage (ES). Available ES exists mainly in boiler steam-water systems, in units' condensed water systems (CW), and in district heating networks (DHN). The goal of the paper is to analysis the ES quantitatively. And ES is characterized by ES coefficient, the maximum ES capacity and ES respond speed for power load. ES coefficient, the key parameter of ES capacity, represents the change in ES when unit process variable changes. For pressure, flow, and temperature variables, three kinds of mechanism methods (volume increment method, equivalent enthalpy drop method, and specific enthalpy increment method) are proposed to calculate ES coefficients. Then, the maximum ES capacity can be obtained by the product of ES coefficient and the limit value of the variable. Finally, ES respond speed for power load can be drawn from simulation. Calculation results and simulations show that ES in CW has small capacity 1.2 GJ but fast speed; ES in boiler has larger capacity 2.6 GJ and slower respond speed; ES in DHN is 374 GJ, which is two orders of magnitude larger than the previous two, and the response is relatively fast. Therefore, recommendations to increase power load flexibility are using ES in boiler and DHN to reduce fuel fluctuation when power load change frequently, using ES in CW to reduce load responding time, and using ES in DHN to expand load regulation range.

Economic Benefit Evaluation of Waste Heat Recovery in Coal-fired CHP System Based on Exergoeconomic Analysis

As one of the main energy-saving measures and an important part of the power industry, CHP (combined heat and power) has achieved rapid development in recent years, which have the advantages of low heat loss, flexible operation mode, and cascade utilization of energy compared with heating boilers and traditional power plants. However, there is a lack of reasonable evaluation of CHP systems, due to the difference in energy quality of heat and electricity. It is urgent to establish considerable and reasonable evaluation indexes of CHP systems. In addition, in the actual operation of CHP plant, a large amount of waste heat is released into the environment, and there is still room for further improvement in the waste heat utilization. In this paper, an exergoeconomic analysis model of CHP system with circulating fluidized bed boiler is established, and the economic benefits of waste heat recovery in CHP systems are studied. After the application of waste heat recovery, the system exergy efficiency increased from 32.94% to 34.14%. The unit exergoeconomic cost of electricity and process steam did not change much, but the unit exergoeconomic cost of heating decreased by 17.1%, which indicates the economic benefits of waste heat recovery.

Heat–power decoupling technologies for coal-fired CHP plants: Operation flexibility and thermodynamic performance

Heat–power decoupling is important for combined heat and power (CHP) plants because it improves their operational flexibility. In this study, off-design and thermodynamic analysis models are developed to examine and compare the operational flexibility improvement and thermodynamic performance of heat–power decoupling technologies. Quantitative analyses are then conducted on a 350 MW reference CHP plant. Results show that feasible operation domains are enlarged by heat–power decoupling technologies. Low-pressure turbine (LPT) renovations, such as zero output renovation and that with a bladeless shaft, have the most potential for reducing the feasible minimum power load, followed by electric boilers. Under a heating load of 300 MW, the feasible minimum power loads can be reduced by 71.6, 124.2, 42.4, and 157.7 MW with a heat pump, an electric boiler, a heat storage tank, and LPT renovations, respectively. However, the heating load of LPT renovations is completely coupled with power load, and its feasible operation domain is limited. Moreover, electric boilers decrease the energy and exergy efficiencies of CHP plants. Therefore, the heat storage tank decoupling technology is the preferable energy-saving option, followed by the heat pump decoupling technology.

Thermodynamic analysis of a novel combined heat and power system incorporating a CO2 heat pump cycle for enhancing flexibility

A novel design of combined heat and power (CHP) with improved flexibility was developed in this paper. A CO2 heat pump (HP) cycle has been adopted in the proposed CHP scheme, where the excess self-produced electricity can be converted into district heat through the HP cycle, recovering the waste energy of the exhaust steam in the meantime. The thermal performance of the proposed scheme was examined based on a 300 MW coal-fired CHP unit, compared with the conventional scheme and the scheme with an electric boiler (EB). The results indicate that while 15.0 MW of the generated power is consumed for heating on site and the total heat output remains 300.0 MW, the proposed design can reduce the minimum power output from 170.7 MW to 132.1 MW, which is 16.3 MW less than that of the EB scheme and conduces to dispatching more renewable electricity. And the effective electric efficiency of the new scheme is 4.89 and 7.70 percentage points higher than those of the conventional scheme and EB scheme, respectively. Energy and exergy analyses were conducted to explore the decoupling and energy-saving mechanisms of the novel concept. Besides, the sensitivity of the reformative CHP system was discussed.

Comparative study of flexibility enhancement technologies for the coal-fired combined heat and power plant

The flexibility enhancement of the coal-fired combined heat and power (CHP) plant can contribute to both renewable energy integration and decarbonization. In this research, we classify the flexibility enhancement technologies into the “power to heat (P2H)” mode and “auxiliary heat source (AHS)” mode based on their principles and operational strategies. Then thermodynamic performances of both modes are compared with the designed heat load and one-day loads. After that, the techno-economic analysis is also conducted. Results show that with the designed heat load, the power load factor range of the CHP plant is extended from 54.87%–78.72% to 25.20%–100% with the AHS mode, and to 0–78.72% with the electric boiler. And compared to integration with the heat-only boiler, the coal consumption of CHP plant can be increased by 2.27% with the thermal energy storage (TES) system (Electric boiler), and reduced by 0.78%, 1.85%, 2.33%, 3.34% with the electric boiler, electric heat pump, TES system (Extraction steam) and waste heat recovery, respectively. The techno-economic analysis indicates that during the heating period, the net annual revenues of the TES system and electric boiler are 2.14 M$ and 1.71 M$ higher than that of the heat-only boiler. This study gives a methodology on choosing the technology to enhance the flexibility for the coal-fired CHP plant.

Energy-saving mechanism and parametric analysis of the high back-pressure heating process in a 300 MW coal-fired combined heat and power unit

Comprehensive and parametric analyses were conducted to investigate the thermal characteristic of the high back-pressure (HBP) heating process based on a 300 MW coal-fired combined heat and power (CHP) unit. The results indicated that the HBP design promoted the thermal efficiency of the unit by 5.97% (absolute value) and cut down the standard coal consumption rate by 23.52 g/(kW·h), attributing to the exhaust steam recovery efficiency of 57% and the unit generation power increase of 24.58 MW. On the grounds of the first and second laws of thermodynamics, the detailed energy-saving mechanism of the HBP heating concept was synthetically explored by the analyses of energy and exergy flows and graphical exergy, and the results showed that the HBP heating configuration improved the unit performance by reducing the exhaust steam energy loss and the extraction steam flow rate and raising the exergy efficiency of the heat exchange process. The impacts of the primary parameters (unit generation load, unit heating load, supply & return-water temperatures and turbine back-pressure) on the performance of the HBP-CHP unit were also examined and optimization suggestions were put forward. Besides, the heat and power coupling characteristic of the HBP-CHP unit was discussed.