Green Hydrogen Production from Raw Biogas: A Techno-Economic Investigation of Conventional Processes Using Pressure Swing Adsorption Unit

This paper discusses the techno-economic assessment of hydrogen production from biogas with conventional systems. The work is part of the European project BIONICO, whose purpose is to develop and test a membrane reactor (MR) for hydrogen production from biogas. Within the BIONICO project, steam reforming (SR) and autothermal reforming (ATR), have been identified as well-known technologies for hydrogen production from biogas. Two biogases were examined: one produced by landfill and the other one by anaerobic digester. The purification unit required in the conventional plants has been studied and modeled in detail, using Aspen Adsorption. A pressure swing adsorption system (PSA) with two and four beds and a vacuum PSA (VPSA) made of four beds are compared. VPSA operates at sub-atmospheric pressure, thus increasing the recovery: results of the simulations show that the performances strongly depend on the design choices and on the gas feeding the purification unit. The best purity and recovery values were obtained with the VPSA system, which achieves a recovery between 50% and 60% at a vacuum pressure of 0.1 bar and a hydrogen purity of 99.999%. The SR and ATR plants were designed in Aspen Plus, integrating the studied VPSA model, and analyzing the behavior of the systems at the variation of the pressure and the type of input biogas. The SR system achieves a maximum efficiency, calculated on the LHV, of 52% at 12 bar, while the ATR of 28% at 18 bar. The economic analysis determined a hydrogen production cost of around 5 €/kg of hydrogen for the SR case

Experimental and numerical study of a micro-cogeneration Stirling unit under diverse conditions of the working fluid

Micro-cogeneration Stirling units are promising for residential applications because of high total efficiencies, favorable ratios of thermal to electrical powers and low CO as well as NOx emissions. This work focuses on the experimental and the numerical analysis of a commercial unit generating 8 kW of hot water (up to 15 kW with an auxiliary burner) and 1 kW of electricity burning natural gas. In the experimental campaign, the initial pressure of the working fluid is changed in a range from 9 to 24 barg – 20 barg being the nominal value – while the inlet temperature of the water loop and its mass flow rate are kept at the nominal conditions of, respectively, 50°C and 0.194 kg/s. The experimental results indicate clearly that the initial pressure of the working fluid – Nitrogen – affects strongly the net electrical power output and efficiency. The best performance for the output and efficiency of 943 W and 9.6% (based on the higher heating value of the burnt natural gas) are achieved at 22 barg. On the other hand, the thermal power trend indicates a maximum value of 8420 W at the working pressure of 24 barg, which corresponds to a thermal efficiency of 84.7% (again based on higher heating value). Measurements are coupled to a detailed model based on a modification of the work by Urieli and Berchowitz. Thanks to the tuning with the experimental results, the numerical model allows investigating the profiles of the main thermodynamic parameters and heat losses during the cycle, as well as estimating those physical properties that are not directly measurable. The major losses turn to be the wall parasitic heat conduction from heater to cooler and the non-unitary effectiveness of the regenerator

Modeling and Testing of a Micro-cogeneration Stirling Engine Under Diverse Conditions of the Working Fluid

Abstract Micro-cogeneration Stirling engines are promising for residential applications. This work focuses on the experimental and numerical analyses of a commercial unit generating 8 kW of hot water and 1 kW of electricity burning natural gas. Measurements are coupled to a detailed model based on a modification of Urieli and Berchowitz's work. The results indicate that the thermal efficiency is influenced by the water loop inlet temperature, varying from 90% at 30 °C to 84% at 70 °C (HHV-based). The measured and simulated powers of the engine are in the 900-964 W range depending on the water temperature and differ by less than 4%. Net electric efficiency of the engine is 15% and of the whole cogeneration unit above 9% (HHV-based). Helium instead of Nitrogen as working fluid is expected to increase the performance

Off-design of a CO2-based mixture transcritical cycle for CSP applications: Analysis at part load and variable ambient temperature

This work focuses on the off-design analysis of a simple recuperative transcritical power cycle working with the CO2 + C6F6 mixture as working fluid. The cycle is aircooled and proposed for a state-of-the-art concentrated solar plant with solar salts as heat transfer fluid in a hot region, with a cycle minimum and maximum temperature of 51 degrees C and 550 degrees C at design conditions. The design of each cycle heat exchanger (primary, recuperator and condenser) is carried out in MATLAB with referenced models and the turbine designed in CFD, providing performance maps adopted by the cycle operating in sliding pressure. The off-design of the cycle is developed with a routine simulating the thermodynamic conditions of the cycle at variable ambient temperature and thermal inputs down to 40 % of the nominal value. The results show that the cycle can efficiently run in a wide range of part load conditions and ambient temperatures, from around 0 degrees C to over 40 degrees C, with net electric cycle efficiencies from 45 % to 36 %: according to the control philosophy proposed, the condenser fans are fixed at design speed, while the cycle operates in sliding pressure, when is possible. The results evidence the flexibility and good performances of the proposed system in various operating conditions

Preliminary investigation of the influence of equations of state on the performance of CO2 + C6F6 as innovative working fluid in transcritical cycles

sCO2 power cycle is the most investigated and most promising technology for replacing conventional steam cycle in CSP plants. Nevertheless, the efficiency of sCO2 power cycle is strongly penalized by high ambient temperatures which are typical of favourable CSP locations. This paper focuses on a new working fluid for power cycles which consists of CO2 blended with C6F6. The addition of C6F6 increases the fluid critical temperature allowing for a condensing cycle for ambient temperatures up to 45 °C. The calculated gross mechanical efficiency of the innovative cycle is around 42% when adopting a typical Peng Robinson equation of state with van der Waals mixing rules for a maximum operating temperature of 550 °C and a minimum cycle temperature of 51 °C. This performance varies just of ±0.1% if the prediction of the binary interaction parameter of the Peng Robinson is over- or under-estimated by 50%, but more significantly if other equations of states are adopted (up to 1% points). Moreover, a detailed analysis on the operating conditions of the cycle components highlighted that components design is affected by the adopted EoS. A sensitivity analysis is then performed to identify where the largest differences in predicting the efficiency of the cycle occur

Investigation of a 5Â kW micro-CHP PEM fuel cell based system integrated with membrane reactor under diverse EU natural gas quality

This work investigates the techno-economic assessment of a 5 kW micro-cogeneration system based on membrane reactor and PEM fuel cell flexible towards different natural gas qualities. The flexibility of the system is evaluated for four typical natural gas compositions from different European countries featuring an average condition and three extreme cases. The optimal system design conditions are determined together with performance variation as function of NG composition and load. The sweep gas and vacuum pump are explored as options to reduce the membrane surface area, outlining the efficiency advantages of the former (41.21% vs. 39.24%). Simulations at partial load show that the electric efficiency increases until 60â\u80\u9370% of the load in both cases, then quickly drops. Micro-CHP performance are used as input to determine the specific system target cost (â\u82¬/kW) based on a yearly energy and economic analysis. The first reveals that the primary energy savings is always positive outlining the environmental benefit of FERRET system application respect to the reference separated production. The target cost considering its application to two dwellings is around 2000 â\u82¬/kW

Scarabeus: Supercritical carbon dioxide/alternative fluid blends for efficiency upgrade of solar power plants

The future of Concentrated Solar Power technology relies on significant cost reduction to be competitive against both fossil fuel power stations and renewable technologies as photovoltaics and wind. Most of the research activity on concentrated solar power focuses on supercritical CO2 cycles to increase the solar plant efficiency together with a cost reduction. Recently, several research groups have started investigating the blending of CO2 with small amounts of additives to boost the thermodynamic cycle performance. The SCARABEUS project aims at developing and demonstrating CO2 blends in concentrating solar power plant with maximum temperatures of 700°C, power cycle efficiency above 50% and cost of electricity below 96 €/MWh. The innovative fluid and newly developed components will be validated at a relevant scale (300 kWth) for 300 h in a CSP-like operating environment