•Improvement potential of deep IGCtH are first assessed by advanced exergy analysis.•Efficiency of deep IGCtH are measured and compared by CExC per kg hydrogen as index.•CExC per kg hydrogen ...reduction by 16.4% for deep IGCtH compared with Lurgi SGCtH.•Lowest cost by deep IGCtH and better ability to resist market risk than Lurgi SGCtH.•Carbon tax of 132 RMB/t CO2 for deep IGCtH with 80% CR equalize cost of without CCS.
The deep in-situ gasification based coal-to-hydrogen (deep IGCtH) is attracting attention for its unique advantage in utilizing unrecoverable coal seam. In this paper, its improvement scope in energy conversion and utilization is analyzed using advanced exergy analysis, and the efficiency from cumulative exergy consumption (CExC) perspective and economic competitiveness with Lurgi surface gasification based coal-to-hydrogen (Lurgi SGCtH), coke-oven gas-to-hydrogen (COGtH) and natural gas-to-hydrogen (NGtH) are compared. Results indicate 39.9 % and 25.1 % of the exergy destruction of deep IGCtH and Lurgi SGCtH are unavoidable, while steam methane reforming and coal gasification possess the largest improvable potential, with avoidable endogenous/exogenous destruction of 96.63 MW/81.58 MW and 162.52 MW/151.19 MW, suggesting thermodynamic improvement can also be achieved by improving other components or optimizing process structure in addition to increasing its own efficiency. The CExC of deep IGCtH outputting 1 kg hydrogen is only 83.6 % that of Lurgi SGCtH, indicating it is more efficient route with significantly energy consumption reduction and can better demonstrate its efficiency advantage under large production capacity condition. The deep IGCtH shows only 68.7 % that of Lurgi SGCtH in investment and also presents significant advantage in cost. However, its profitability advantage over NGtH loses with hydrogen price increasing and there exists lower limit on capacity of 0.46 billion Nm3 to maintain cost and profitability competitiveness over COGtH. Furthermore, deep IGCtH shows emission reduction cost advantage over Lurgi SGCtH when capture rate exceeds 80 %, and profitability will not be limited by carbon tax and coal seam thickness within the considered range.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Novel relation between dynamic metabolic rate and PMV provides increased accuracy.•Novel relation between human body exergy consumption rate and PMV.•Novel relation between measured CO2 ...concentration and human exergy consumption.•Model provides better understanding of CO2 impact on thermal comfort assessment.•The minimal value of the human body exergy consumption rate occurs for PMV = −0.02.
The majority of studies dealing with the correlation between human body exergy consumption and thermal comfort use adopted, constant values of metabolic rate for appropriate activity level. Taking into account correlations between metabolic rate and the occupant’s exhaled CO2 volumetric flow rate, this study proposes a novel method for the calculation of metabolic rate using measured CO2 concentration in the indoor air. Using measured values of the air and radiant temperature, relative humidity and air velocity, and calculated values of metabolic rate, the human body exergy consumption rate and corresponding Predicted Mean Vote (PMV) are calculated. Moreover, a novel polynomial relation between them is proposed. Results show that metabolic rate values vary in the range of 0.97 to 1.54 met which leads to significantly wider range of PMV and human body exergy consumption rate comparing to the assumed value of 1.2 met for sedentary school activity. According to the obtained relation, the minimal value of the human body exergy consumption rate occurs for PMV = − 0.02. Results of this study imply that treating CO2 concentration as variable does have an impact on the thermal comfort assessment, providing enhanced correlations between thermal comfort and human body exergy consumption rate.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Deep underground coal gasification (UCG) for making hydrogen can not only utilize the rich deep coal resources in China and convert difficult-to-mine or uneconomical deep coal resources into ...hydrogen, but also is a potential low-cost hydrogen production route. Based on the world’s only kilometer-scale deep UCG experimental data and combined with Aspen Plus process simulation, this study analyzes the energy utilization of hydrogen production through deep UCG using the advanced exergy analysis method. In comparison with the commercialized Lurgi surface coal gasification route, the energy consumption levels of the two hydrogen production routes were compared using the cumulative exergy consumption per unit of hydrogen output as an indicator. The research results show that under the hydrogen production capacity of 1.2 billion Nm3/a, the total exergy losses from raw materials to products in deep UCG for hydrogen production are 451.79 MW. Advanced exergy analysis can effectively quantify the exergy losses that can
This paper reviews methods that measure mineral resource depletion based on cumulative exergy consumption approaches. It focuses on the exergy replacement cost (ERC), which measures the amount of ...exergy society would have to consume in order to re-concentrate an extracted and processed mineral to the point that it can be once more exploited by future generations. The ERC, which was originally only suitable for non-fuel minerals, was adapted and extended in 2016, by changing the focus of the ERC from the chemical composition of the resource to its function, to include fossil fuel depletion. This paper discusses the impact of these new developments and identifies conceptual and methodological weaknesses that need to be addressed for the ERC to find widespread use in exergy analysis and in order to assess the sustainability of mineral policy from the grave to the cradle.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The clean and efficient energy production from municipal solid waste (MSW) is highly desirable due to increasing energy demand and environmental concerns. In this study, four incineration- (S1) and ...gasification-based (S2 with combustion boiler, S3 with gas turbine/combined cycle and S4 with internal combustion engine) MSW treatments were compared using methods of environmental life cycle assessment (LCA) and exergetic life cycle assessment (ELCA). LCA was applied to measure the environmental performances and ELCA was supplemented to reflect the thermodynamics efficiencies. Afterwards, cumulative degree of perfection (CDP) and abatement exergy (AbatCExC) efficiency of the considered systems were also calculated to determine the imperfection and environmental sustainability of the processes. Results showed that gasification-based systems were effective to mitigate the environmental impacts of acidification, nutrient enrichment, and photochemical ozone formation potential, but caused higher global warming impacts. The S3 system exhibited the best performance from both environmental and exergetic perspective, due to its high net efficiency of electricity generation and low exhaust emission into air. Results from ELCA indicated that the rest two gasification-based systems (S2 and S4) were inefficient as compared to MSW direct incineration, mainly due to auxiliary energy consumption for MSW pretreatment and more conversion steps. The CDP and AbatCExC of the systems in descending order was expressed as S3 system > S1 system > S2 system > S4 system.
•Four incineration and gasification WtE systems were modeled and compared.•Gasification gas turbine/CC showed best environmental and exergetic performance.•Gasification systems showed low environmental burdens but high GW potential.•MSW direct incineration showed high CExC and CDP efficiency.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Thermodynamic and pressure drop models can accurately predict system performance.•Effect of electric consumption is negligible in terms of energy consumption.•An exergy consumption index is proposed ...for rational evaluation of system performance.•The priority is to adjust liquid flow rate and top temperature in the optimization.
In this study, the thermodynamic and pressure drop models of the humidification–dehumidification (HDH) system are developed and verified by the experimental results. The effect of operating parameters on the system performance is investigated. The parametric analysis indicates that the optimum point of the energy efficiency may appear in some cases. The pressure drop in the system increases with the air and liquid mass flow rates and the liquid top temperature. The influence of electric consumption on the system overall performance is evaluated from the different point of view (energy and exergy). In terms of energy consumption, the proportion of electric consumption in the total energy consumption is small with an average of 9.9%. The effect of electric energy consumption is negligible in many cases. In terms of exergy consumption, the average proportion of electric consumption is 29.4%, and the highest is 40.6%. The electric energy consumption has significant influences on the overall energy efficiency. Furthermore, numerical optimization is performed to achieve the minimum specific exergy consumption (SEXC). It can be concluded that, in the performance optimization of the HDH system, the priority is to adjust the liquid mass flow rate and liquid top temperature. The minimum values of the optimized SEXC are 222.0 kJ/kg.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Cumulative exergy consumption is an innovative method that can help to evaluate different energy use problems in crop production process. In this study, cumulative exergy approach was applied for ...evaluate the tomato production process. In this context, open field productions in South Marmara and Tokat, and also greenhouse structures in Antalya were assessed by cumulative exergy consumption for tomato production in Turkey. The results showed that, Tokat is the best region for tomato production in open field. Cumulative degree of perfection and renewability indicator for tomato production in this region were 1.62 and 0.38, respectively. In this study, cumulative exergy consumption showed that water consumption in open field and also electricity consumption in greenhouse conditions are high. Fossil fuel is the main sources in these regions for pumpping water and also electricity generation. As a new case, hydroelectricity energy supply is provided instead of fossil energy source for irrigation system and electricity generation. The results showed that when the hydroelectricity source was applied for irrigation system and electricity generation, the best region based on renewability indicator is Antalya (greenhouse condition). As a result, the cumulative exergy consumption approach is an effective method for increasing the renewability of crop production processes.
•Renewability (Ir) analysis as a new approach for crop production, was applied.•Open field condition has the higher Ir value than the greenhouse structure.•The CExC value of irrigation and electricity usage in the tomato production is high.•In the new case, irrigation and electricity use were provided with hydraulic energy.•In the new case, greenhouse has the higher Ir value than the open field condition.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The demand for H2 increases rapidly with the gradual recognition of the potential of H2 as an important secondary energy. At present, coal gasification is the main way to obtain hydrogen on a large ...scale and at a low cost in China. The underground coal gasification (UCG), as a kind of in-situ utilization technology that can exploit the unreachable deep coal resources, could become an alternative H2 production pathway. This paper presents comparative study of energy utilization and resource consumption in H2 production by UCG and typical surface coal gasification (SCG) technology, namely Lurgi fixed bed gasification, with 1.2 billion Nm3/a throughput of H2 as example, to offer corresponding data support. The efficiency and the amount of resources consumed in constructing and operating each coal-to-hydrogen system under different conditions have been researched from exergetic point of view, which is not reported in existing literatures. In this paper, the exergy efficiency is calculated to be 40.48% and 40.98% for hydrogen production using UCG and SCG. The result indicates the competitiveness of UCG in the field of hydrogen production comparing with widely used coal gasification technology. The resource consumption is measured by cumulative exergy consumption (CExC), which is 8.17E+10 MJ and 6.57E+10 MJ for H2 production from UCG and SCG. The result shows that although the H2 production from UCG has higher CExC, it can significantly reduce the resource consumption of equipment comparing with H2 production from SCG, indicating its advantage in total investment. It is found that the exergy efficiency increases with the rise in H2O-to-O2 and O2-to-CO2 ratio, while the value of CExC decreases with the appreciation of H2O-to-O2 ratio yet increases as the O2-to-CO2 ratio rises. In addition, the sensitivity analysis of production capacity reveals that the exergy efficiency gap and CExC gap between hydrogen production by UCG and SCG diminishes at smaller scale production capacities, showing that UCG is more suitable for small-scale hydrogen production.
•A resource consumption comparison of H2 production from UCG and SCG is conducted.•Exergy is analyzed with 1.2 billion Nm3/a throughput of H2 as example.•Exergy efficiency of UCG-H2 reaches 40.48%, comparable to 40.98% for SCG-H2.•UCG-H2 significantly reduces CExC of equipment compared to SCG-H2.•Effects of key operational parameters on system's performances are investigated.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The separate collection of Used Cooking Oil (UCO) is gaining popularity through several countries in Europe. An appropriate management of UCO waste stream leads to substantial benefits. In this ...study, we analyse two different possibilities of UCO energy reuse: the direct feed to a reciprocating internal combustion engine (ICE) for cogeneration purpose, and the processing to generate biodiesel. Concerning biodiesel production, we analyse four among conventional and innovative technologies, characterised by different type and amount of used chemicals, heat and electricity consumptions and yields. We perform a systematic evaluation of environmental benefits and drawbacks by applying life cycle assessment (LCA) analysis to compare the alternatives.
For the impact assessment, two methods are selected: the Global Warming Potential (GWP) and Cumulative Exergy Consumption (CExC). Results related only to the processing phases (i.e. not including yet the avoided effects) show that the recovery of UCO in cogeneration plant has in general lower values in terms of environmental impacts than its employment in biodiesel production.
When products and co-products substitution are included, the savings obtained by the substitution of conventional diesel production, in the biodiesel cases, are significantly higher than the avoided effects for electricity and heat in the cogeneration case. In particular, by using the UCO in the biodiesel production processes, the savings vary from 41.6 to 54.6 GJex per tUCO, and from 2270 to 2860 kg CO2eq per tUCO for CExC and GWP, respectively. A particular focus is put on sensitivity and uncertainty analyses. Overall, high uncertainty of final results for process impacts is observed, especially for the supercritical methanol process. Low uncertainty values are evaluated for the avoided effects. Including the uncertain character of the impacts, cogeneration scenario and NaOH catalysed process of biodiesel production result to be the most suitable solutions from the process impacts and avoided effects perspective.
•Life cycle assessment (LCA) of energy recovery from used cooking oil (UCO).•Cogeneration vs. biodiesel production comparison.•Cogeneration requires less impactful processing processes.•Biodiesel production allows higher benefits for conventional diesel substitution.•Cogeneration and supercritical biodiesel production are the most uncertain processes to evaluate.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•The energy and exergy performance of different heating systems are analyzed and compared;•Stratum ventilation is applicable and suitable for heating in sleeping environment;•Stratum ventilation ...shows higher energy efficiency under heating mode.
To provide a highly efficient heating for the residential buildings, different heating systems, including the floor and ceiling heating, wall radiator heating and stratum ventilation heating, are compared based on a typical sleeping environment in this study. Performance indices, including occupied zone predicted mean vote (OPMV), energy consumption and exergy consumption, are analyzed under different conditions. The results show that stratum ventilation heating performs better than the conventional floor, ceiling and wall radiator heating in terms of energy and exergy consumptions. Firstly, under stratum ventilation heating, the OPMV equals zero at a low supply air temperature (20.0°C for stratum ventilation heating at the supply air angle of 45° and 19.7°C for stratum ventilation heating mode at the supply air angle of 75°). Secondly, stratum ventilation heating consumes less energy than the floor, ceiling or wall radiator heating of identical OPMV increments. In addition, compared with the floor, ceiling, wall radiator heating and stratum ventilation heating at the supply air angle of 45°, the energy-saving ratio of stratum ventilation heating at the supply air angle of 75° reaches 29.7%, 21.2%, 22.4% and 4.2% respectively when OPMV equals zero. Lastly, for stratum ventilation heating, the supply and return water temperatures in the air handling unit are significantly lower. Therefore, a lower exergy consumption is realized under stratum ventilation heating in comparison with the conventional floor, ceiling and wall radiator heating.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
