A power plant for integrated waste energy recovery from liquid air energy storage and liquefied natural gas

Liquefied natural gas(LNG)is regarded as one of the cleanest fossil fuel and has experienced significant developments in recent years.The liquefaction process of natural gas is energy-intensive,while the regasification of LNG gives out a huge amount of waste energy since plenty of high grade cold energy(-160℃)from LNG is released to sea water directly in most cases,and also sometimes LNG is burned for regasification.On the other hand,liquid air energy storage(LAES)is an emerging energy storage technology for applications such as peak load shifting of power grids,which generates 30%-40%of compression heat(-200℃).Such heat could lead to energy waste if not recovered and used.The recovery of the compression heat is technically feasible but requires additional capital investment,which may not always be economically attractive.Therefore,we propose a power plant for recovering the waste cryogenic energy from LNG regasification and compression heat from the LAES.The challenge for such a power plant is the wide working temperature range between the low-temperature exergy source(-160℃)and heat source(-200℃).Nitrogen and argon are proposed as the working fluids to address the challenge.Thermodynamic analyses are carried out and the results show that the power plant could achieve a thermal efficiency of 27%and 19%and an exergy efficiency of 40%and 28%for nitrogen and argon,respectively.Here,with the nitrogen as working fluid undergoes a complete Brayton Cycle,while the argon based power plant goes through a combined Brayton and Rankine Cycle.Besides,the economic analysis shows that the payback period of this proposed system is only 2.2 years,utilizing the excess heat from a 5 MW/40 MWh LAES system.The findings suggest that the waste energy based power plant could be co-located with the LNG terminal and LAES plant,providing additional power output and reducing energy waste.

Integrated construction technology for natural gas gravity drive and underground gas storage

Based on the mechanisms of gravity displacement,miscibility,viscosity reduction,and imbibition in natural gas flooding,an integrated reservoir construction technology of oil displacement and underground gas storage(UGS)is proposed.This paper systemically describes the technical connotation,site selection principle and optimization process of operation parameters of the gas storage,and advantages of this technology.By making full use of the gravity displacement,miscibility,viscosity reduction,and imbibition features of natural gas flooding,the natural gas can be injected into oil reservoir to enhance oil recovery and build strategic gas storage at the same time,realizing the win-win situation of oil production and natural gas peak shaving.Compared with the gas reservoir storage,the integrated construction technology of gas storage has two profit models:increasing crude oil production and gas storage transfer fee,so it has better economic benefit.At the same time,in this kind of gas storage,gas is injected at high pressure in the initial stage of its construction,gas is injected and produced in small volume in the initial operation stage,and then in large volume in the middle and late operation stage.In this way,the gas storage wouldn’t have drastic changes in stress periodically,overcoming the shortcomings of large stress variations of gas reservoir storage during injection-production cycle due to large gas injection and production volume.The keys of this technology are site selection and evaluation of oil reservoir,and optimization of gravity displacement,displacement pressure,and gas storage operation parameters,etc.The pilot test shows that the technology has achieved initial success,which is a new idea for the rapid development of UGS construction in China.

Real-time Risk-averse Dispatch of an Integrated Electricity and Natural Gas System via Condi-tional Value-at-risk-based Lookup-table Ap-proximate Dynamic Programming

The real-time risk-averse dispatch problem of an integrated electricity and natural gas system(IEGS)is studied in this paper.It is formulated as a real-time conditional value-at-risk(CVaR)-based risk-averse dis-patch model in the Markov decision process framework.Because of its stochasticity,nonconvexity and nonlinearity,the model is difficult to analyze by traditional algorithms in an acceptable time.To address this non-deterministic polynomial-hard problem,a CVaR-based lookup-table approximate dynamic programming(CVaR-ADP)algo-rithm is proposed,and the risk-averse dispatch problem is decoupled into a series of tractable subproblems.The line pack is used as the state variable to describe the impact of one period’s decision on the future.This facilitates the reduction of load shedding and wind power curtailment.Through the proposed method,real-time decisions can be made according to the current information,while the value functions can be used to overview the whole opti-mization horizon to balance the current cost and future risk loss.Numerical simulations indicate that the pro-posed method can effectively measure and control the risk costs in extreme scenarios.Moreover,the decisions can be made within 10 s,which meets the requirement of the real-time dispatch of an IEGS.Index Terms—Integrated electricity and natural gas system,approximate dynamic programming,real-time dispatch,risk-averse,conditional value-at-risk.

Techno-economic assessment of a chemical looping splitting system for H2 and CO Co-generation

The natural gas(NG)reforming is currently one of the low-cost methods for hydrogen production.However,the mixture of H2 and CO_(2) in the produced gas inevitably includes CO_(2) and necessitates the costly CO_(2) separation.In this work,a novel double chemical looping involving both combustion(CLC)and sorption-enhanced reforming(SE-CLR)was proposed towards the co-production of H2 and CO(CLC-SECLRHC)in two separated streams.CLC provides reactant CO_(2) and energy to feed SECLRHC,which generates hydrogen in a higher purity,as well as the calcium cycle to generate CO in a higher purity.Techno-economic assessment of the proposed system was conducted to evaluate its efficiency and economic competitiveness.Studies revealed that the optimal molar ratios of oxygen carrier(OC)/NG and steam/NG for reforming were recommended to be 1.7 and 1.0,respectively.The heat integration within CLC and SECLRHC units can be achieved by circulating hot OCs.The desired temperatures of fuel reactor(FR)and reforming reactor(RR)should be 850
C and 600
C,respectively.The heat coupling between CLC and SECLRHC units can be realized via a jacket-type reactor,and the NG split ratio for reforming and combustion was 0.53:0.47.Under the optimal conditions,the H2 purity,the H2 yield and the CH4 conversion efficiency were 98.76%,2.31 mol mol-1 and 97.96%,respectively.The carbon and hydrogen utilization efficiency respectively were 58.60% and 72.45%in terms of the total hydrogen in both steam and NG.The exergy efficiency of the overall process reached 70.28%.In terms of the conventional plant capacity(75 × 103 t y^(-1))and current raw materials price(2500$t^(-1)),the payback period can be 6.2 years and the IRR would be 11.5,demonstrating an economically feasible and risk resistant capability.

Numerical modeling and assessment of natural gas pipeline separation in China: the data from Henan Province

China’s natural gas market is focusing on price reform and aims to reconstruct vertically integrated industrial chains in the future.Based on the mixed complementarity problem model of gas markets with nodes in Henan Province,China,as an example,this paper applies numerical modeling to simulate the effects of social welfare and equilibrium prices on nodes in two scenarios:pipeline integration and pipeline separation.The findings reveal the following:(1)Pipeline separation yields greater overall social welfare than pipeline integration,with the welfare shifting from gas producers to consumption markets.(2)Pipeline separation lowers the equilibrium consumption prices by driving competition among gas supply sources.(3)Pipeline separation will increase the contribution of natural gas to primary energy.

Analysis and Economic Evaluation of Hourly Operation Strategy Based on MSW Classification and LNG Multi-Generation System

In this study,a model of combined cooling,heating and power system with municipal solid waste(MSW)and liquefied natural gas(LNG)as energy sources was proposed and developed based on the energy demand of a large community,andMSW was classified and utilized.The systemoperated by determining power by heating load,and measures were taken to reduce operating costs by purchasing and selling LNG,natural gas(NG),cooling,heating,and power.Based on this system model,three operation strategies were proposed based on whether MSW was classified and the length of kitchen waste fermentation time,and each strategy was simulated hourly throughout the year.The results showed that the strategy of MSW classified and centralized fermentation of kitchen waste in summer(i.e.,strategy 3)required the least total amount of LNG for the whole year,which was 47701.77 t.In terms of total annual cost expenditure,strategy 3 had the best overall economy,with the lowest total annual expenditure of 2.7730×108 RMB at LNG and NG unit prices of 4 and 4.2 RMB/kg,respectively.The lower heating value of biogas produced by fermentation of kitchen waste from MSW being classified was higher than that of MSW before being classified,so the average annual thermal economy of the operating strategy of MSW being classified was better than that of MSW not being classified.Among the strategies in which MSW was classified and utilized,strategy 3 could better meet the load demand of users in the corresponding season,and thus this strategy had better thermal economy than the strategy of year-round fermentation of kitchen waste(i.e.,strategy 2).The hourly analysis data showed that the net electrical efficiency of the system varies in the same trend as the cooling,heating and power loads in all seasons,while the relationship between the energy utilization efficiency and load varied from season to season.This study can provide guidance for the practical application of MSW being classified in the system.

Analysis of Driving Factors of Natural Gas Consumption in China: Based on Regional Integration and LMDI Method

In recent years,China has developed rapidly in terms of natural gas.Driven by regional economic integration,a regional natural gas market composed of neighboring provinces and cities has taken shape gradually,and it tends to grow toward the same direction in policy formulation,resource coordination,facility construction and market expansion.Based on the factors such as geographical location,economic conditions and natural gas consumption,this thesis tends to conduct a horizontal comparative analysis on the economic development conditions,natural gas consumption characteristics and natural gas pipeline network density of the three regions with obvious regional integration feature in China.Then according to LMDI,four core indicators,namely economic growth effect,energy intensity effect,energy structure effect,and substitution effect are selected.The thesis is expected to explore the contribution of different indicators to the growth of natural gas consumption in these three different regions.According to the results,it can be concluded that the driving factors of natural gas consumption differ greatly among regions.Specifically speaking,the more developed the economy is,the greater the contribution of the energy substitution effect to natural gas consumption will be,and the contribution of the economic growth effect to natural gas consumption will be smaller.Despite that the contribution of energy intensity in different regions shows slight difference,the energy structure contributes the least effect,which further explains the current differences in China’s natural gas consumption characteristics and the reasons behind.

Reliability Assessment of Integrated Electricity and Natural Gas Transmission Systems in Presence of Power-to-gas and Combined Heat and Power Technologies

Assessing the reliability of integrated electricity and gas systems has become an important issue due to the strong dependence of these energy networks through the power-to-gas(P2G)and combined heat and power(CHP)technologies.The current work,initially,presents a detailed energy flow model for the integrated power and natural gas system in light of the P2G and CHP technologies.Considering the simultaneous load flow of networks,a contingency analysis procedure is proposed,and reliability is assessed through sequential Monte Carlo simulations.The current study examines the effect of independent and dependent operation of energy networks on the reliability of the systems.In particular,the effect of employing both P2G and CHP technologies on reliability criteria is evaluated.In addition,a series of sensitivity analysis are performed on the size and site of these technologies to investigate their effects on system reliability.The proposed method is implemented on an integrated IEEE 24-bus electrical power system and 20-node Belgian natural gas system.The simulation procedure certifies the proposed method for reliability assessment is practical and applicable.In addition,the results prove connection between energy networks through P2G and CHP technologies can improve reliability of networks if the site and size of technologies are properly determined.

Hydrate formation and distribution within unconsolidated sediment:Insights from laboratory electrical resistivity tomography

Laboratory visual detection on the hydrate accumulation process provides an effective and low-cost method to uncover hydrate accumulation mechanisms in nature.However,the spatial hydrate distribution and its dynamic evolutionary behaviors are still not fully understood due to the lack of methods and experimental systems.Toward this goal,we built a two-dimensional electrical resistivity tomography(ERT)apparatus capable of measuring spatial and temporal characteristics of hydrate-bearing porous media.Beach sand(0.05–0.85 mm)was used to form artificial methane hydrate-bearing sediment.The experiments were conducted at 1°C under excess water conditions and the ERT data were acquired and analyzed.This study demonstrates the utility of the ERT method for hydrate mapping in laboratory-scale.The results indicate that the average electrical conductivity decreases nonlinearly with the formation of the hydrate.At some special time-intervals,the average conductivity fluctuates within a certain scope.The plane conductivity fields evolve heterogeneously and the local preferential hydrate-forming positions alternate throughout the experimental duration.We speculate that the combination of hydrate formation itself and salt-removal effect plays a dominant role in the spatial and temporal hydrate distribution,as well as geophysical parameters changing behaviors during hydrate accumulation.

Optimal Scheduling of Electrical Energy Systems Using a Fluid Dynamic Analogy

The electricity-gas transformation problem and related intrinsic mechanisms are considered.First,existing schemes for the optimization of electricity-gas integrated energy systems are analyzed through consideration of the relevant literature,and an Electricity Hub(EH)for electricity-gas coupling is proposed.Then,the distribution mechanism in the circuit of the considered electricity-gas integrated system is analyzed.Afterward,a mathematical model for the natural gas pipeline is elaborated according to the power relationship,a node power flow calculation method,and security requirements.Next,the coupling relationship between them is implemented,and dedicated simulations are carried out.Through experimental data,it is found that after 79 data iterations,the optimization results of power generation and gas purchase cost in the new system converge to$54,936 in total,which is consistent with the data obtained by an existing centralized optimization scheme.However,the new proposed optimization scheme is found to be more flexible and convenient.

Optimization of Thermal and Electrical Appliance Loads in Residential and Commercial Buildings with Demand Side Monitoring

Energy demand-supply mechanism with the load shape for both residential and commercial buildings in the Province of Ontario and Nigeria is studied with demand side monitoring of energy consumption. Thermal and electrical loads are characterized by certain predictor variables, including the consumers’ behavioural pattern, power ratings of energy appliances and weather conditions. The proposed bottom-up approach is capable of providing low-volume electricity and natural gas consumers, in a fully deregulated energy market, with competitive energy saving advantage, based on corrective monitoring of independent users’ demand loads. Special application of the bottom-up model-based facility characterization of demands for thermal comfort and indoor air qualityin a developing energy sector like Nigeria enables the development of planning tool for the proposed integration of renewable power systems. The developed DSMonitorTM app is capable of deploying an effective smart grid technology tool towards an improved building energy demand-supply balance at the individual end-user level.

Cascading Failure Propagation Simulation in Integrated Electricity and Natural Gas Systems

The sharp increase in the total installed capacity of natural gas generators has intensified the dynamic interaction between the electricity and natural gas systems,which could induce cascading failure propagation across the two systems that deserves intensive research.Considering the distinct time response behaviors of the two systems,this paper discusses an integrated simulation approach to simulate the cascading failure propagation process of integrated electricity and natural gas systems(IEGSs).On one hand,considering instantaneous re-distribution of power flows after the occurrence of disturbance or failure,the steady-state AC power flow model is employed.On the other hand,gas transmission dynamics are represented by dynamic model to capture the details of its transition process.The interactions between the two systems,intensified by energy coupling components(such as gas-fired generator and electricity-driven gas compressor)as well as the switching among the operation modes of compressors during the cascading failure propagation process,are studied.An IEGS composed of the IEEE 30-bus electricity system and a 14-node 15-pipeline gas system is established to illustrate the effectiveness of the proposed simulation approach,in which two energy sub-systems are coupled by compressor and gas-fired generator.Numerical results clearly demonstrate that heterogeneous interactions between electricity and gas systems would trigger the cascading failure propagation between the two coupling systems.

Stochastic Dynamic Economic Dispatch of Wind-integrated Electricity and Natural Gas Systems Considering Security Risk Constraints

As the proportion of wind power generation increases in power systems,it is necessary to develop new ways for wind power accommodation and improve the existing power dispatch model.The power-to-gas technology,which offers a new approach to accommodate surplus wind power,is an excellent way to solve the former.Hence,this paper proposes to involve power-to-gas technology in the integrated electricity and natural gas systems(IEGSs).To solve the latter,on one hand,a new indicator,the scale factor of wind power integration,is introduced into the wind power stochastic model to better describe the uncertainty of grid-connected wind power;on the other hand,for quantizing and minimizing the impact of the uncertainties of wind power and system loads on system security,security risk constraints are established for the IEGS by the conditional value-at-risk method.By considering these two aspects,an MILP formulation of a security-risk based stochastic dynamic economic dispatch model for an IEGS is established,and GUROBI obtained from GAMS is used for the solution.Case studies are conducted on an IEGS consisting of a modified IEEE 39-bus system and the Belgium 20-node natural gas system to examine the effectiveness of the proposed dispatch model.

Multi-period integrated natural gas and electric power system probabilistic optimal power flow incorporating power-to-gas units

The increasing adoption of gas-fired power plants directly strengthens the coupling between electric power and natural gas systems. Current industrial practice in optimal power flow for electric power systems has not taken the security constraints of gas systems into consideration, resulting in an overly-optimistic solution. Meanwhile, the operation of electric power and natural gas systems is coupled over multiple periods because of the ramp rate limits of power generators and the slow dynamical characteristics of gas systems. Based on these motivations, we propose a multi-period integrated natural gas and electric power system probabilistic optimal power flow(M-GEPOPF) model, which includes dynamic gas flow models. To address the uncertainties originating from wind power and load forecasting, a probabilistic optimal power flow(POPF) calculation based on a three-point estimate method(3 PEM) is adopted. Moreover, power-togas(Pt G) units are employed to avoid wind power curtailment and enable flexible bi-directional energy flows between the coupled energy systems. An integrated IEEE RTS 24-bus electric power system and the Belgian 20-node natural gas system are employed as a test case to verify the applicability of the proposed M-GEPOPF model, and to demonstrate the potential economic benefits of Pt G units.

Integrated operational planning of hydrothermal power and natural gas systems with large scale storages

The growing installation of natural gas fired power plants has increased the integration of natural gas and electricity sectors. This has driven the need investigate the interactions among them and to optimize energy resources management from a centralized planning perspective. Thus, a combined modeling of the reservoirs involved in electric power and gas systems and their locations on both networks are essential features to be considered in the operational planning of energy resources.This paper presents a modeling and optimization approach to the operational planning of electric power and natural gas systems, taking into account different energy storage facilities, such as water reservoirs, natural gas storages and line packs of pipelines. The proposed model takes advantage of captures both energy systems synergy and their associated networks. This approach identifies the interactions between the energy storage facilities and their economic impact over their optimal scheduling. The results show the benefits of an integrated operational planning of electric power and natural gas systems, the close interdependency between the energy resources stored in both systems, and the effects of a combined scheduling.

Optimal Operation of Integrated Energy Systems Subject to Coupled Demand Constraints of Electricity and Natural Gas

This paper proposes a hybrid multi-objective optimization and game-theoretic approach(HMOGTA)to achieve the optimal operation of integrated energy systems(IESs)consisting of electricity and natural gas(E&G)utility networks,multiple distributed energy stations(DESs),and multiple energy users(EUs).The HMOGTA aims to solve the coordinated operation strategy of the electricity and natural gas networks considering the demand characteristics of DESs and EUs.In the HMOGTA,a hierarchical Stackelberg game model is developed for generating equilibrium strategies of DESs and EUs in each district energy network(DEN).Based on the game results,we obtain the coupling demand constraints of electricity and natural gas(CDCENs)which reflect the relationship between the amounts and prices of electricity and cooling(E&C)that DESs purchase from utility networks.Furthermore,the minimization of conflicting costs of E&G networks considering the CDCENs are solved by a multi-objective optimization method.A case study is conducted on a test IES composed of a 20-node natural gas network,a modified IEEE 30-bus system,and 3 DENs,which verifies the effectiveness of the proposed HMOGTA to realize fair treatment for all participants in the IES.

Robust optimization for improving resilience of integrated energy systems with electricity and natural gas infrastructures

The integration of natural gas in electricity network requires a more reliable operating plan for increasing uncertainties in the whole system. In this paper, a threestage robust optimization model is proposed for resilient operation of energy system which integrates electricity and natural gas transmission networks with the objective of minimizing load curtailments caused by attacks. Nonconvex constrains are linearized in order to formulate the dual problem of optimal energy flow. Then, the proposed three-stage problem can be reformulated into a two-stage mixed integer linear program(MILP) and solved by Benders decomposition algorithm. Numerical studies on IEEE30-bus power system with 7-node natural gas network and IEEE 118-bus power system with 14-node natural gas network validate the feasibility of the proposed model for improving resilience of integrated energy system. Energy storage facilities are also considered for the resiliency analysis.

Coordinated Dispatch of Integrated Electricity-Natural Gas System and the Freight Railway Network

With the significant development of liquefied natural gas(LNG)rail transport,the railway system is increasingly more closely connected with the integrated electricity-natural gas system(IEGS).To coordinate the economic operations of the two systems,this paper innovatively proposes a coordinated dispatch model of IEGS with LNG infrastructures and a freight railway network with LNG transport.First,an operational scheduling model of the railway network,considering energy consumption,is put forward for both LNG transmission and ordinary freight transport.Then,the coordinated dispatch problem of IEGS and the railway network is formulated into a mixed-integer linear programming model via the big M method and a modified incremental linearization approach.Finally,a bi-level optimization algorithm based on generalized benders decomposition(GBD)is presented to solve the coordinated dispatch problem due to the restrictions on exchanging private information.Case studies demonstrate the effectiveness of the proposed model and algorithm as well as the potential benefit for wind power accommodation.

Integrated coordination scheduling framework of electricity-natural gas systems considering electricity transmission N—1 contingencies and gas dynamics

This paper discusses a security-constrained integrated coordination scheduling framework for an integrated electricity-natural gas system(IEGS),in which both tight interdependence between electricity and natural gas transmission networks and their distinct dynamic characteristics at different timescales are fully considered.The proposed framework includes two linear programming models.The first one focuses on hour-based steady-state coordinated economic scheduling on power outputs of electricity generators and mass flow rates of natural gas sources while considering electricity transmission N-1 contingencies.Using the steady-state mass flow rate solutions of gas sources as the initial value,the second one studies second-based slow gas dynamics and optimizes pressures of gas sources to ensure that inlet gas pressure of gas-fired generator is within the required pressure range at any time between two consecutive steady-state scheduling.The proposed framework is validated via an IEGS consisting of an IEEE 24-bus electricity network and a15-node 14-pipeline natural gas network coupled by gasfired generators.Numerical results illustrate the effectiveness of the proposed framework in coordinating electricity and natural gas systems as well as achieving economic and reliable operation of IEGS.