Emission operational strategy for combined cooling,heating, and power systems

Integrated Energy Systems (IES), as technology that use thermal activated components to recover waste heat, are energy systems that offer key solution to global warming and energy security through high overall energy efficiency and better fuel use. Combined Cooling, Heating, and Power (CCHP) Systems are IES that use recovered thermal energy from the prime mover to produce heating and cooling for the building. The CCHP operational strategy is critical and it has to be considered in a well designed system since it defines the ultimate goal for the benefits expected from the system. One of the most common operational strategies is the cost-oriented strategy, which allows the system to operate at the lowest cost. A primary energy strategy (PES) optimizes energy consumption instead of cost. However, as a result of the worldwide concern about global warming, projects that target reduction of greenhouse gas (GHG) emissions have gained a lot of interest. Therefore, for a CCHP system, an emission strategy (ES) would be an operational strategy oriented to minimize emission of pollutants. In this study, the use of an ES is proposed for CCHP systems targeted to reduce emission of pollutants. The primary energy consumption (PEC) reduction and carbon dioxide (CO₂) emission reduction obtained using the proposed ES are compared with results obtained from the use of a PES. Results show that lower emission of CO₂ is achieved with the ES when compared with the PES, which prove the advantage of the ES for the design of CCHP systems targeted to emissions reduction.     

Evaluation of the performance of combined cooling,heating, and power systems with dual power generation units

The benefits of using a combined cooling, heating, and power system with dual power generation units (D-CCHP) is examined in nine different U.S. locations. One power generation unit (PGU) is operated at base load while the other is operated following the electric load. The waste heat from both PGUs is used for heating and for cooling via an absorption chiller. The D-CCHP configuration is studied for a restaurant benchmark building, and its performance is quantified in terms of operational cost, primary energy consumption (PEC), and carbon dioxide emissions (CDE). Cost spark spread, PEC spark spread, and CDE spark spread are examined as performance indicators for the D-CCHP system. D-CCHP system performance correlates well with spark spreads, with higher spark spreads signifying greater savings through implementation of a D-CCHP system. A new parameter, thermal difference, is introduced to investigate the relative performance of a D-CCHP system compared to a dual PGU combined heat and power system (D-CHP). Thermal difference, together with spark spread, can explain the variation in savings of a D-CCHP system over a D-CHP system for each location. The effect of carbon credits on operational cost savings with respect to the reference case is shown for selected locations.     

Analysis of combined cooling,heating, and power systems based on source primary energy consumption

Combined cooling, heating, and power (CCHP) is a cogeneration technology that integrates an absorption chiller to produce cooling, which is sometimes referred to as trigeneration. For building applications, CCHP systems have the advantage to maintain high overall energy efficiency throughout the year. Design and operation of CCHP systems must consider the type and quality of the energy being consumed. Type and magnitude of the on-site energy consumed by a building having separated heating and cooling systems is different than a building having CCHP. Therefore, building energy consumption must be compared using the same reference which is usually the primary energy measured at the source. Site-to-source energy conversion factors can be used to estimate the equivalent source energy from site energy consumption. However, building energy consumption depends on multiple parameters. In this study, mathematical relations are derived to define conditions a CCHP system should operate in order to guarantee primary energy savings.     

Optimal design and 4E assessment of typical combined cooling,heating and power systems considering the effects of energy price fluctuation

Although as an advanced energy utilization approach, the performance of combined cooling, heating, and power (CCHP) system is susceptible to its configuration and operation strategy. Energy price will also affect the system performance indirectly by influencing the system's design scheme. In this paper, a linear programming (LP) based optimization model is formulated to obtain the optimal design scheme that minimizes the annual total cost of typical CCHP systems, and a comprehensive assessment framework involving economic, energy, exergy, and ecological (4E) aspects is established to assess the system performance roundly. Taking a CCHP project in Xian, China as the specific case, the design and assessment of the CCHP system are completed and sensitivity analyses for two steps, namely configuration design step and operation strategy design step, are carried out to explore the impacts of energy price fluctuation on the design scheme and performance of the system. In this process, the coupling relationship between the purchase price of natural gas and electricity are considered, and as a special form of energy price, the effects of the feed‐in tariff are also discussed. The results show that the performance of the CCHP system is superior to the separate generation (SG) system in 4E aspects, reducing the running and maintenance cost, primary energy consumption, and greenhouse gas emissions by 18.63%, 24.77%, and 31.88%, respectively, and promoting the exergy efficiency by 30.87%. The feed‐in tariff lower than or equal to the electricity price will have positive effects on the overall performance of the CCHP system, and a lower natural gas price and a higher electricity price are benefit for playing the advantages of the system.     

Multiple effects of energy storage units on combined cooling,heating and power (CCHP) systems

Albeit numerous studies discussing manifold issues of combined cooling, heating and power (CCHP) systems, there is still lack of theoretical studies indicating to what extent the energy mismatch and the deviating working conditions affect the CCHP performance, absence of reports systematically summarizing the multiple effects of energy saving units (ESUs), and deficiency of research quantifying the benefits from ESUs to energy savings. The shortage of such studies will confuse some CCHP designers when a CCHP system is designed. Therefore, in this research, theoretical discussions have been undertaken about the energy mismatch issue between CCHP systems and their users as well as the multiple effects of ESUs on CCHP systems. An improved calculational method of energy storage rate (ESR) has been adopted to evaluate the energy savings performance of CCHP systems. Two general heat‐to‐electricity ratios (R_user for CCHP users and R_CCHP for CCHP systems) have been used to quantify the energy mismatch between CCHP systems and their users. In the regime of ‘priority of providing cooling’, the ESR reaches its maximum when R_user is equal to R_CCHP. Otherwise, the ESR tends to decrease rapidly, especially when the electrical demand must be supplemented from the grid. Furthermore, when the CCHP system produces more electricity than required, the payment mode of extra electricity from the CCHP system will significantly affect the ESR. Therefore, it is imperative to reach an international consensus regarding the dispose of extra CCHP products. The theoretical analyses also corroborate the advantages of incorporating an ESU into a CCHP system. The ESU enables the CCHP system components to operate at their optimal working conditions. Meanwhile, the power generation unit and the absorption refrigerator capacities can then be reduced. Moreover, the ESU also promotes the productivity of electricity and ensures an undiminished ESR regardless of what extra electricity payment mode is adopted. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of cooling,heating, and power systems based on site energy consumption

Feasibility of cooling, heating, and power systems frequently is based on economic considerations such as energy prices. However, a most adequate feasibility of CHP systems must be based on energy consumption followed by economic considerations. CHP systems designs must yield economical savings, but more importantly must yield real energy savings based on the best energy performance. For CHP systems, energy savings is related to primary energy and not to site energy. This paper presents a mathematical analysis demonstrating that CHP systems increase the site energy consumption (SEC). Increasing the SEC could yield misleading results in the economic feasibility of CHP systems. Three different operation modes are evaluated: (a) cooling, heating, and power; (b) heating and power; and (c) cooling and power, to represent the operation of the system throughout the year. Results show that CHP systems increase site energy consumption; therefore primary energy consumption (PEC) should be used instead of SEC when designing CHP systems.     

冷热电联产系统的发展及前景

1前言能源的价格、电网的稳定性、能量的品质、空气的品质以及全球气候的改变,是21世纪我们面临的严重问题。随着经济和社会的发展,这些问题将变得更加尖锐。在传统的利用燃料产生电力的过程中,将近三分之二的输入能量没有有效利用就被释放到环境中,能量损失十分严重。利用总能     

Energy,exergy and thermoeconomic analysis of a combined cooling,heating and power (CCHP) system with gas turbine prime mover

In this paper energy, exergy and thermoeconomic analysis of a combined cooling, heating and power (CCHP) system has been performed. Applying the first and second laws of thermodynamics and economic analysis, simultaneously, has made a powerful tool for the analysis of energy systems such as CCHP systems. The system integrates air compressor, combustion chamber, gas turbine, dual pressure heat recovery steam generator (HRSG) and absorption chiller to produce cooling, heating and power. In fact, the first and second laws of thermodynamics are combined with thermoeconomic approaches. Next, computational analysis is performed to investigate the effects of below items on the fuel consumption, values of cooling, heating and net power output, the first and second laws efficiencies, exergy destruction in each of the components and total cost of the system. These items include the following: air compressor pressure ratio, turbine inlet temperature, pinch temperatures in dual pressure HRSG, pressure of steam that enters the generator of absorption chiller and process steam pressure. Decision makers may find the methodology explained in this paper very useful for comparison and selection of CCHP systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Multi-criteria analysis of combined cooling,heating and power systems in different climate zones in China

The design and operation of combined cooling, heating and power (CCHP) systems are greatly dependent upon the seasonal atmospheric conditions, which determine thermal and power demands of buildings. This paper presents a mathematical analysis of CCHP system in comparison to separate system. The corresponding primary energy consumption in thermal demand management (TDM) and electrical demand management (EDM) operation modes are deduced. Three relative criteria, primary energy saving (PES), CO₂ emission reduction (CO₂ER), and annual total cost saving (ATCS) are employed to evaluate the respective performances of CCHP systems for a hypothetical building in five different climate zones from the technical, environmental and economic aspects. The results indicate that CCHP system in TDM mode in the cold area, where the building requires more heating during the year, achieves more benefit over separate system while CCHP system in EDM mode suits the building having stable thermal demand in mild climate zone.     

某热电厂实施冷热电联产的节能分析

通过对热电联产冷分产及冷热电联产能源消耗的计算分析比较,进一步论述在热电厂热电联产基础上发展冷热电联产的可行性和合理性,结合实例说明发展冷热电联产所产生的经济性、节能性和环保性,并为其他热电厂的节能改造提出建议,     

Integrated energy systems based on cascade utilization of energy

Focusing on the traditional principle of physical energy utilization, new integration concepts for combined cooling, heating and power (CCHP) system were identified, and corresponding systems were investigated. Furthermore, the principle of cascade utilization of both chemical and physical energy in energy systems with the integration of chemical processes and thermal cycles was introduced, along with a general equation describing the interrelationship among energy levels of substance, Gibbs free energy of chemical reaction and physical energy. On the basis of this principle, a polygeneration system for power and liquid fuel (methanol) production has been presented and investigated. This system innovatively integrates a fresh gas preparation subsystem without composition adjustment process (NA) and a methanol synthesis subsystem with partial-recycle scheme (PR). Meanwhile, a multi-functional energy system (MES) that consumes coal and natural gas as fuels simultaneously, and co-generates methanol and power, has been presented. In the MES, coal and natural gas are utilized synthetically based on the method of dual-fuel reforming, which integrates methane/steam reforming and coal combustion. Compared with conventional energy systems that do not consider cascade utilization of chemical energy, both of these systems provide superior performance, whose energy saving ratio can be as high as 10%–15%. With special attention paid to chemical energy utilization, the integration features of these two systems have been revealed, and the important role that the principle of cascade utilization of both chemical and physical energy plays in system integration has been identified.     

Sizing analysis of a combined cooling,heating, and power system for a small office building using a wood waste biomass‐fired Stirling engine

When wood chips are available and used to fuel a combined cooling, heating, and power (CCHP) waste heat recovery system, they can represent an economically viable source of biomass energy that can meet a facility's electric and thermal demands. Using a Stirling engine as the CCHP prime mover provides several important advantages over conventional internal combustion engines including no additional processing of the waste wood chips, a potentially higher thermal efficiency, flexibility of fuel sources, and low maintenance. This study shows how the operational characteristics of a constant output, biomass‐fired, Stirling engine‐based CCHP system are affected by the performance of the individual components, including the prime mover, heat recovery system, auxiliary boiler, absorption chiller, and heating coil unit The results are assessed by examining the primary energy consumption and operational cost compared with a reference case. The analysis provides insight on the prime mover sizing and selection of each component to properly implement the system. In addition to examining the effects of each component, the effect of excess electricity production and buyback are considered. Copyright © 2010 John Wiley & Sons, Ltd.     

太阳能与燃煤联合发电技术及其应用前景

介绍了太阳能与燃煤联合发电技术原理及工程应用,综合分析了联合发电系统不同集成方案的热经济性,给出了太阳能与燃煤联合发电技术的应用前景,提出了我国发展太阳能与燃煤联合发电技术的建议。通过对太阳能与燃煤联合发电系统的性能分析及工程实例表明,太阳能场与燃煤机组回热系统相结合的方式,运行稳定,经济性较好,特别是太阳能场取代1段抽汽的集成方案较为理想,具有很好的发展前景。     

Performance comparison of combined cooling heating and power system in different operation modes

Operation mode of combined cooling heating and power (CCHP) system determines its energetic and environmental performances. This paper analyzes the energy flows of CCHP system and separated production (SP) system. The fuel energy consumptions of CCHP system following electrical demand management (EDM) and thermal demand management (TDM) are deduced respectively. Three indicators: primary energy saving, exergy efficiency and CO₂ emission reduction, are employed to evaluate the performances of CCHP system for a commercial building in Beijing, China. The feasibility analysis shows that the performance of CCHP system is strictly dependent upon building energy demands. The selection of CCHP operation modes is systemically based on building loads, CCHP system and local SP system. The calculation results conclude that CCHP system in winter under EDM achieves more benefits than in summer. The sensitivity discussion indicates that the coefficient of performance for cooling and the efficiency of electricity generation are the most sensitive variables to the energetic and environmental performances of CCHP system.     

冷热电联供系统运行模式优化

以最小运行费用和最小一次能耗率为目标函数,基于非线性规划和动态规划,利用MATLAB对冷热电联供系统的运行模式进行优化。通过与常规供能方式的比较,为建筑供能方案初设提供辅助设计。     

Simulation and economic evaluation of biomass gasification with sets for heating,cooling and power production

In this work, syngas was used directly as fuel source for the renewable CCHP system, which can be producted through biomass gasification process. The advantages and limitation of entrained flow gasifier are compared, followed by discussion on the key parameters that are critical for the optimum production of syngas. Gasification agent of 450 °C temperature and 30 atm pressure has been proposed as a optical solution to a entrained flow gasifier using air as gasification agent at 0.27 ER (oxygen equivalence ratio), in that it provides a syngas of 5.665 MJ/m³ LHV and up to 77% gasification efficiency. Depending on the key parameters of gasification process, the properties of syngas produced can be varied. It is thus essential to thoroughly understand the cogeneration system to identify the suitable methods for a renewable CCHP system. These process was simulated using Aspen Plus to perform the rigorous material and energy balances. The results obtained from simulation and experiment agreed well. This paper later focused on economic evaluation of the entire process, as well as the environmental benefits. The renewable CCHP system could able to attain lower CO₂ and SO₂ emission with total energy efficiency and gas yield of 75.43% and 2.476 m³/kg respectively.     

Primary energy and economic analysis of combined heating, cooling and power systems

In this paper, the primary energy consumption and the economic viability of a combined heating, cooling and power (CHCP) system are derived. The focus is on small-scale applications in the range below 100 kW_H/70 kW_C/58 kW_el. CHCP is discussed between the boundaries of combined heating and power (CHP) and combined cooling and power (CCP) using a lumped parameter model. The method used is independent of a specific load profile for a building; only the full-load hours for heating and cooling are needed to predict the economic viability. German data is used for the example. A sensitivity analysis reveals the parameters with the highest impact on the primary energy consumption and the energy costs. The primary energy factors, the energy prices and the electric efficiency of the CHP are the dominating parameters. Increasing electricity prices favour the introduction of CHP and CHCP systems whereas increasing gas prices inhibit it. The energy cost analysis is extended to an economic analysis taking maintenance and investment costs into account. One result of this paper is a simple diagram which shows how many annual operation hours are needed for heating and cooling with CHCP to be more economical than a reference system.     

A concept of combined cooling,heating and power system utilising solar power and based on reversible solid oxide fuel cell and metal hydrides

In energy systems, multi-generation including co-generation and tri-generation has gained tremendous interest in the recent years as an effective way of waste heat recovery. Solid oxide fuel cells are efficient power plants that not only generate electricity with high energy efficiency but also produce high quality waste heat that can be further used for hot and chilled water production. In this work, we present a concept of combined cooling, heating and power (CCHP) energy system which uses solar power as a primary energy source and utilizes a reversible solid oxide fuel cell (R-SOFC) for producing hydrogen and generating electricity in the electrolyser (SOEC) and fuel cell (SOFC) modes, respectively. The system uses “high temperature” metal hydride (MH) for storage of both hydrogen and heat, as well as “low temperature” MH's for the additional heat management, including hot water supply, residential heating during winter time, or cooling/air conditioning during summer time.The work presents evaluation of energy balances of the system components, as well as heat-and-mass transfer modelling of MH beds in metal hydride hydrogen and heat storage system (MHHS; MgH₂), MH hydrogen compressor (MHHC; AB₅; A = La + Mm, BNi + Co + Al + Mn) and MH heat pump (MHHP; AB₂; A = Ti + Zr, BMn + Cr + Ni + Fe). A case study of a 3 kWe R-SOFC is analysed and discussed. The results showed that the energy efficiencies are 69.4 and 72.4% in electrolyser and fuel cell modes, respectively. The round-trip COP's of metal hydride heat management system (MHHC + MHHP) are close to 40% for both heating and cooling outputs. Moreover, the tri-generation leads to an improvement of 36% in round-trip energy efficiency as compared to that of a stand-alone R-SOFC.     

基于压缩空气储能的新型冷热电联供系统性能研究

为了解决用户负荷需求在时间上的变动和传统冷热电联供（Combine Cooling, Heating & Power, CCHP）系统大部分时间处于非设计工况下运行导致系统的能源利用效率较低的问题,提出了一种耦合压缩空气储能系统（Compressed Air Energy Storage system, CAES）和蓄热装置的新型CCHP系统（CAES based CCHP system,CAES CCHP）,建立系统的热力学模型,在给定的充、放电工作条件下对CAES CCHP系统的热力学性能进行分析,并对影响该系统性能的CAES压气机压缩比、透平进气口压力、流经CAES的烟气质量流量3个关键参数进行敏感性分析。研究结果表明：CAES CCHP系统能实现冷热电灵活调控,且系统的CAES功转换效率为57.41%,一次能源利用率、一次节能率及火用效率分别为76.22%,24.84%和31.97%,比传统的CCHP系统分别提高10.97%,18.15%和7.58%。