Exergy analyses and parametric optimizations for different cogeneration power plants in cement industry

The cement production is an energy intensive industry with energy typically accounting for 50–60% of the production costs. In order to recover waste heat from the preheater exhaust and clinker cooler exhaust gases in cement plant, single flash steam cycle, dual-pressure steam cycle, organic Rankine cycle (ORC) and the Kalina cycle are used for cogeneration in cement plant. The exergy analysis for each cogeneration system is examined, and a parameter optimization for each cogeneration system is achieved by means of genetic algorithm (GA) to reach the maximum exergy efficiency. The optimum performances for different cogeneration systems are compared under the same condition. The results show that the exergy losses in turbine, condenser, and heat recovery vapor generator are relatively large, and reducing the exergy losses of these components could improve the performance of the cogeneration system. Compared with other systems, the Kalina cycle could achieve the best performance in cement plant.     

Development and analysis of a novel biomass-based integrated system for multigeneration with hydrogen production

Energy and exergy analyses of an integrated system based on anaerobic digestion (AD) of sewage sludge from wastewater treatment plant (WWTP) for multi-generation are investigated in this study. The multigeneration system is operated by the biogas produced from digestion process. The useful outputs of this system are power, freshwater, heat, and hydrogen while there are some heat recoveries within the system for improving efficiency. An open-air Brayton cycle, as well as organic Rankine cycle (ORC) with R-245fa as working fluid, are employed for power generation. Also, desalination is performed using the waste heat of power generation unit through a parallel/cross multi-effect desalination (MED) system for water purification. Moreover, a proton exchange membrane (PEM) electrolyzer is used for electrochemical hydrogen production option in the case of excess electricity generation. The heating process is performed via the rejected heat of the ORC's working fluid. The production rates for products including the power, freshwater, hydrogen, and hot water are obtained as 1102 kW, 0.94 kg/s, 0.347 kg/h, and 1.82 kg/s, respectively, in the base case conditions. Besides, the overall energy and exergy efficiencies of 63.6% and 40% are obtained for the developed system, respectively.     

Life Cycle Energy Assessment of biohydrogen production via biogas steam reforming: Case study of biogas plant on a farm in Serbia

The aim of this paper is to demonstrate and to quantify energy flows in a life cycle of biogas to biohydrogen production, starting from feedstock materials via anaerobic digestion, biogas upgrading, biohydrogen production, to the end of biogas system (application of digestate as fertilizer in agriculture). The performance of the biogas plant of Mirotin dairy farm in Serbia has been assessed. According to Life Cycle Energy Assessment approach, results obtained in this study have shown that biohydrogen production via biogas steam reforming has negative energy balance (with ?16,837 GJ). It has also been demonstrated that this process is energy unsustainable in an environmental context. In future analysis it would be necessary to consider the other aspects of sustainability, e.g. the economical and social factors in order to estimate the overall sustainability of the biogas utilization pathways, especially having in mind that the technology of converting biogas to hydrogen is still in the development phase.     

废水处理产生的沼气回收技术应用与实践

厌氧UASB反应器在去除废水中有机物过程中可产生大量沼气。基于啤酒废水可生化程度高,在厌氧处理过程中产生大量的可再生的绿色能源生物质能沼气。综合污水处理和沼气利用技术,对厌氧UASB反应器产生的沼气进行收集预处理后,通过沼气锅炉燃烧产生蒸汽再回用到啤酒生产中,从而达到节能减排的效果。     

Optimization Potentials for the Waste Heat Recovery of a Gas-Steam Combined Cycle Power Plant Based on Absorption Heat Pump

A new waste heat recovery system is presented to recover exhausted steam waste heat from the steam turbine by absorption heat pump(AHP) in a gas-steam combined cycle(GSCC) power plant. The system can decrease energy consumption and further improve the energy utilization. The performance evaluation criteria are calculated, and exergy analysis for key components are implemented in terms of the energy and exergy analysis theory. Besides, the change of these criteria is also revealed before and after modification. The net power output approximately increases by 21738 kW, and equivalent coal consumption decreases by 5.58 g/kWh. A 1.81% and 1.92% increase in the thermal and exergy efficiency is respectively obtained in the new integrated system as the heating load is 401095 kJ at 100% condition. Meanwhile, the appropriate extraction parameters for heating have been also analyzed in the two systems. The proposed scheme can not only save energy consumption but also reduce emission and gain great economic benefit, which is proven to be a huge potential for practical application.     

Engineering design and exergy analyses for combustion gas turbine based power generation system

This paper presents the engineering design and theoretical exergetic analyses of the plant for combustion gas turbine based power generation systems. Exergy analysis is performed based on the first and second laws of thermodynamics for power generation systems. The results show the exergy analyses for a steam cycle system predict the plant efficiency more precisely. The plant efficiency for partial load operation is lower than full load operation. Increasing the pinch points will decrease the combined cycle plant efficiency. The engineering design is based on inlet air-cooling and natural gas preheating for increasing the net power output and efficiency. To evaluate the energy utilization, one combined cycle unit and one cogeneration system, consisting of gas turbine generators, heat recovery steam generators, one steam turbine generator with steam extracted for process have been analyzed. The analytical results are used for engineering design and component selection.     

高有机负荷下的稻草两级/单级CSTR厌氧消化工艺性能研究

文章以稻草为原料,采用两级和单级厌氧消化工艺,在较高有机负荷(100,120,140 g/L)下对稻草的消化性能进行了研究。研究结果表明:当有机负荷分别为100,120,140 g/L时,两级厌氧消化系统的产甲烷效率分别比单级厌氧消化系统提高了8.8%,11.5%,11.8%;两级厌氧消化系统的产甲烷量主要集中在第一级,随着有机负荷的提高,第二级的产甲烷量占比逐渐增加;两级厌氧消化系统的物质转化率比单级厌氧消化系统更高,并且两级厌氧消化系统中的大部分物质在第一级去除,与产气效率的结果相一致;两级和单级厌氧消化系统在3个高有机负荷条件下均可以稳定运行。     

Impact of single versus multiple policy options on the economic feasibility of biogas energy production: Swine and dairy operations in Nova Scotia

The economic feasibility of on-farm biogas energy production was investigated for swine and dairy operations under Nova Scotia, Canada farming conditions, using net present value (NPV), internal rate of return (IRR), and payback period (PP) economic decision criteria. In addition, the effects of selected environmental and “green” energy policy schemes on co-generation of on-farm biogas energy production and other co-benefits from anaerobic digestion of livestock manure were investigated. Cost-efficiencies arising from economies of scale for on-farm anaerobic biogas production were found for swine farms, and less so for dairy production systems. Without incentive schemes, on-farm biogas energy production was not economically feasible across the farm size ranges studied, except for 600- and 800-sow operations. Among single policy schemes investigated, green energy credit policy schemes generated the highest financial returns, compared to cost-share and low-interest loan schemes. Combinations of multiple policies that included cost-share and green energy credit incentive schemes generated the most improvement in financial feasibility of on-farm biogas energy production, for both swine and dairy operations.     

Changing old habits: The case of feeding patterns in anaerobic digesters

A non-linear programming model was developed to maximize the economic profit from an anaerobic co-digester. The model consists of a combination of technical and economic equations, linked through the biogas production variable. Five scenarios were simulated. These differed with regard to substrate inlet mass flow rate, organic loading rate and hydraulic retention time. The impact on biogas production was investigated and an economic analysis was undertaken based on the concepts of profitability and Net Present Value. The model results indicate that varying the substrate inlet mass flow rate and organic loading rate could have a positive impact on the profitability of co-digesters in Flanders. This can be achieved either by increasing the interval time between feedstock input, or by feeding individual streams of feedstock separately into the system, while at the same time reducing the hydraulic retention time.     

联合循环参数和系统结构优化研究

研究了如何提高余热锅炉型三压再热联合循环系统的效率,应用分析的方法建立了系统效率数学模型,以联合循环系统效率最高作为系统性能的评判标准。在亚临界范围内,对余热锅炉的蒸汽参数进行了优化;针对余热锅炉进气温度对余热锅炉性能的影响进行分析,在此基础上提出燃气轮机排气部分回热利用,并研究了回热利用对联合循环效率的影响。计算结果表明:经余热锅炉优化和排气部分回热利用,在基本负荷下,PG9351FA机组的联合循环热效率可提高1.33%;在75%和50%的负荷下,效率分别提高2.11%和4.17%;而具有再热的GT26机组热效率高达60.73%。     

Energy analysis of the system of two-stage anaerobic processing of liquid organic waste with production of hydrogen- and methane-containing biogases

In recent years, public attention has been increasingly attracted to solving two inextricably linked problems - preventing the depletion of natural resources and protecting the environment from anthropogenic pollution. The annual consumption of livestock waste for biogas production is about 240 thousand m³ per year, which is 0.17% of the total manure produced at Russian agricultural enterprises. At present, the actual use of organic waste potentially suitable for biogas production is 2–3 orders of magnitude lower than the existing potential for organic waste. Currently, hydrogen energy is gaining immense popularity in the world due to the problem of depletion of non-renewable energy sources - hydrocarbons, and environmental pollution caused by their increasing consumption. Of particular interest is the dark process of producing hydrogen-containing biogas in the processing of organic waste under anaerobic conditions, which allows you to take advantage of both energy production and solving the problem of organic waste disposal. An energy analysis of a two-stage anaerobic liquid organic waste processing system with the production of hydrogen- and methane-containing biogases based on experimental data obtained in a laboratory plant with increased volume reactors was performed. The energy efficiency of the system is in the range of 1.91–2.74. Maximum energy efficiency was observed with a hydraulic retention time of 2.5 days in a dark fermentation reactor. The cost of electricity to produce 1 m³ of hydrogen was 1.093 kW·h with a hydraulic retention time of 2.5 days in the dark fermentation reactor. When the hydraulic retention time in the dark fermentation reactor was 1 day, the specific (in ratio to the processing rate of organic waste) energy costs to produce of 1 m³ of hydrogen were minimal in the considered hrt range, and amounted to 26 (W/m³ of hydrogen)/(m³ of waste/day). Thus, the system of two-stage anaerobic processing of liquid organic waste to produce hydrogen and methane-containing biogases is an energy-efficient way to both produce hydrogen and process organic waste.     

Investigation of green hydrogen production and development of waste heat recovery system in biogas power plant for sustainable energy applications

In this study, biogas power production and green hydrogen potential as an energy carrier are evaluated from biomass. Integrating an Organic Rankine Cycle (ORC) to benefit from the waste exhaust gases is considered. The power obtained from the ORC is used to produce hydrogen by water electrolysis, eliminate the H₂S generated during the biogas production process and store the excess electricity. Thermodynamic and thermoeconomic analyses and optimization of the designed Combined Heat and Power (CHP) system for this purpose have been performed. The proposed study contains originality about the sustainability and efficiency of renewable energy resources. System design and analysis are performed with Engineering Equation Solver (EES) and Aspen Plus software. According to the results of thermodynamic analysis, the energy and exergy efficiency of the existing power plant is 28.69% and 25.15%. The new integrated system's energy, exergy efficiencies, and power capacity are calculated as 41.55%, 36.42%, and 5792 kW. The total hydrogen production from the system is 0.12412 kg/s. According to the results of the thermoeconomic analysis, the unit cost of the electricity produced in the existing power plant is 0.04323 $/kWh. The cost of electricity and hydrogen produced in the new proposed system is determined as 0.03922 $/kWh and 0.181 $/kg H₂, respectively.     

Economics of anaerobic digestion in organic agriculture: Between system constraints and policy regulations

During its pioneer-stage in Germany, the generation of power and heat from anaerobic digestion (AD) was predominantly developed on organic farms. However, biogas production in organic agriculture (OR) never expanded to the same extent as in conventional farming (CV). Besides various other aspects, this appears to be mainly due to economic reasons related to system-specific production requirements. Therefore, this article analyses the framework conditions of organic biogas generation and assesses its monetary implications on production economics. The structural and economic comparison of organic and conventional generation of power from biogas displays systematic constraints for AD in OR and identifies advantages of conventional biogas plants, particularly concerning lower capital and biomass input costs. Moreover, frequently changing policy regulations, further aggravating the economic situation for biogas production in both farming systems, are reflected. Our study shows that the recent developments of political frameworks will inhibit biogas investments for nearly all types of biogas plants in Germany. Finally, an alternative evaluation approach for organic AD systems, considering monetary benefits from agronomic effects of an integrated biogas generation in organic agriculture is discussed.     

Hydrogen production at centralized utilization of agricultural waste

There is a problem of utilization of a large amount of organic waste in the agro-industrial complex. Most of the waste is generated on livestock farms (56%) and crop production (35.6%). Centralized biogas plants are a good solution for efficient processing of agricultural waste and biofuel production. An analysis of the possibilities of cow manure utilizing and dry biomass of amaranth with the subsequent hydrogen production was implemented for Tatarstan Republic. The diagram of five large facilities utilizing waste from 7 to 10 districts included in the region is introduced.The diagram of steam catalytic conversion of biogas is specified. The introduced hydrogen production scheme includes: collection of plant waste and manure of livestock complexes for centralized recycling (the optimal mixture of dry biomass of Amaranthus retroflexus L. leaves and cow manure for organic dry matter is 1:1.5); mixture preparation and ultrasonic treatment at a frequency of 22 kHz and an exposure intensity of 10 W/cm2; anaerobic digestion in the mesophilic mode at a temperature of 310 K, the hydraulic retention time is 12 days; the compressor supplying the resulting biogas into the gasholder for intermediate storage; purification of biogas from carbon dioxide, hydrogen sulfide and other impurities in the scrubber; steam methane reforming: the biomethane is compressed by a compressor to a pressure of 15 atm., then fed to the reformer, heated, mixed with steam in the ratio H2O/CH4 = 2.5 and subjected to conversion at a temperature of 1073 K and a pressure of 1 atm., before exiting, the resulting gas is cooled to 573 K; the catalytic reactor for carrying out a water vapor conversion reaction in which a mixture of carbon monoxide and steam is converted, the products are hydrogen and carbon dioxide; purification of the obtained hydrogen to a purity of 99.99% vol. In the short-cycle adsorption system; hydrogen supply to the consumer. It is possible to utilize of 4.4 million tons of waste annually, and also to produce 107,341 kg/day of hydrogen with a purity of 99.99% by volume.     

Design and thermodynamic assessment of a biomass gasification plant integrated with Brayton cycle and solid oxide steam electrolyzer for compressed hydrogen production

In this paper, a comprehensive thermodynamic evaluation of an integrated plant with biomass is investigated, according to thermodynamic laws. The modeled multi-generation plant works with biogas produced from demolition wood biomass. The plant mainly consists of a biomass gasifier cycle, clean water production system, hydrogen production, hydrogen compression, gas turbine sub-plant, and Rankine cycle. The useful outputs of this plant are hydrogen, electricity, heating and clean water. The hydrogen generation is obtained from high-temperature steam electrolyzer sub-plant. Moreover, the membrane distillation unit is used for freshwater production, and also, the hydrogen compression unit with two compressors is used for compressed hydrogen storage. On the other hand, energy and exergy analyses, as well as irreversibilities, are examined according to various factors for examining the efficiency of the examined integrated plant and sub-plants. The results demonstrate that the total energy and exergy efficiencies of the designed plant are determined as 52.84% and 46.59%. Furthermore, the whole irreversibility rate of the designed cycle is to be 37,743 kW, and the highest irreversibility rate is determined in the biomass gasification unit with 12,685 kW.     

Photo-fermentative hydrogen production from cheese whey: Engineering of a mixed culture process in a semi-continuous,tubular photo-bioreactor

This work approaches the engineering of photo fermentative hydrogen production from cheese whey, for the scale-up of photo-bioreactors. Firstly, a brief review has been performed to identify the optimal reactor configuration as well as the main literature lacks. Results of the review analysis suggest that tubular photobioreactors are effective for the photo fermentation process. On the other hand, one of the main drawbacks to the scale-up of the proposed systems is the wide use of pure cultures, which requires aseptic environments and carefully controlled conditions. Based on the critical evaluation of the state of the art, a semi-continuous tubular photobioreactor, performing mixed culture hydrogen production from cheese whey, under unsterile conditions, was started up. Due to the lack of studies in this field, the case study was developed to provide a methodology for the reactor start-up, which represents the most critical phase of its operation. Preliminary tests were performed to choose the optimal operating conditions. To assess the effectiveness of cheese whey, results were compared to those obtained from a glucose based synthetic substrate, under steady state conditions. Experimental outcomes showed that the optimal Hydraulic Retention Time was 2 days and the most appropriate recirculation/pumping system consisted of an intermittent peristaltic pump. The semi-continuous feeding of cheese whey resulted in 87 mL/L d of hydrogen, which was similar to the productivity obtained under glucose feeding. The characterization of the residual organic content further indicated the possible accumulation of polyhydroxyalcanohates, which was estimated to constitute about the 40% of the total residual COD. These results further addressed the identification of key points to be better investigated to promote the effective photo fermentation scale-up for cheese whey valorization, such as the enhancement of the illumination conditions as well as the search for strategies to improve the uniform exposure of microbial cells to light.     

Multi-objective optimization and exergoeconomic analysis of a multi-generation system based on biogas-steam reforming

In the current work, a new design of a multi-generation integrated energy system powered by biogas energy is proposed, assessed, and optimized. To scrutinize the workability of the offered system, energy, exergy, exergo-economic, and economic investigations have been applied as robust tools to the evaluation of the system. Moreover, to boost the rate of hydrogen production rate, the steam reforming method and purification process are integrated into the systems. It is found that the designed multi-generation integrated energy system is able to generate 108.7 kW, 888.7 kW, and 703.3 kg/h, power, cooling load, and hydrogen, sequentially. Besides, it is determined that the energy and exergy efficiencies of the system are about 31.51% and 31.14%, sequentially. Furthermore, a comprehensive parametric evaluation is employed to appraise the influences of key variables on the operation of the system and relying on its achieved outcomes, two different optimization styles are established. From the optimization outcomes, it is remarked that in the multi-objective optimization mode, a TCOP of 16.23 S/GJ and a net power of 158.21 KW, are achievable.     

System optimization for effective hydrogen production via anaerobic digestion and biogas steam reforming

To construct a system for the effective hydrogen production from food waste, the conditions of anaerobic digestion and biogas reforming have been investigated and optimized. The type of agitator and reactor shape affect the performance of anaerobic digestion reactors. Reactors with a cubical shape and hydrofoil agitator exhibit high performance due to the enhanced axial flow and turbulence as confirmed by simulation of computational fluid dynamics. The stability of an optimized anaerobic digestion reactor has been tested for 60 days. As a result, 84 L of biogas is produced from 1 kg of food waste. Reaction conditions, such as reaction temperature and steam/methane ratio, affect the biogas steam reforming reaction. The reactant conversions, product yields, and hydrogen production are influenced by reaction conditions. The optimized reaction conditions include a reaction temperature of 700 °C and H₂O/CH₄ ratio of 1.0. Under these conditions, hydrogen can be produced via steam reforming of biogas generated from a two-stage anaerobic digestion reactor for 25 h without significant deactivation and fluctuation.     

Simulation of a solar‐biogas hybrid energy system for heating,fuel supply,and power generation

Biogas production from organic wastes has been widely utilized for several decades, but maintaining right temperature for anaerobic bacteria is a challenge. In order to overcome the inhibition of the bacteria growth and biogas production due to the low temperature, a solar‐biogas hybrid energy system for heating, fuel supply, and power generation has been proposed for converting domestic garbage into biogas in a rural area of China. In this system, the solar energy has been included as one of the heating sources during an anaerobic digestion process. A mathematical model has been developed to evaluate the influence of system operating characteristics. Based on the simulation results, the biogas production rate, thermal efficiency, temperature of the digester, energy distributions in the system, optimal operating parameters, economic efficiency, and thermodynamic characteristics of the system were analyzed. The impact of solar irradiation on the efficiency of the system was also studied. According to the results, in cloudy days, the reactor volume and solar collector area greatly influenced the steady energy supply. In winter, the produced biogas is mostly utilized by the aided boiler to maintain the proper organic mixture temperature in the bioreactor. Heat loss from bioreactor dramatically increases the organic mixture volume. Per simulation, the longest return on the investment of this type of the biogas system is about 5.54 years, and the shortest return on the investment is less than 4 years if the battery is removed and the electric grid can be used. Therefore, in this study, the feasibility of a hybrid energy system for converting domestic garbage into energy has been validated. Copyright © 2017 John Wiley & Sons, Ltd.     

Thermodynamic and exergoeconomic analysis of energy recovery system of biogas from a wastewater treatment plant and use in a Stirling engine

The aim of this research it is to show how the biogas biomethanisation from primary and secondary treatment of activated sludge from a wastewater treatment plant (WWTP), can be an alternative renewable energy option from fossil fuels, which offers competitive advantages and points out new horizons for the use of this fuel. This will allow to achieve some important priorities of energy plans in EU countries: to reduce the organic matter deposited in landfills and CO₂ emissions and to find viable solutions to minimize the environmental impact of sewage sludge (SS).This study analyses the biogas combustion and energy recovery processes from a thermodynamic, thermoeconomic and exergetic point of view.The results show that the boiler of the process is the main source of irreversibility and exergy destruction. Moreover, the energy and exergy economic value of exhaust gases from the combustion chamber, are significant and worthwhile to be exploited. For this reason, the present study explores the applicability and suitability of integrating a Stirling engine in such process. The study reveals that it is possible to create a small micro-cogeneration system which leads to sustainable waste management and energy savings in the treatment plant itself.