Optimization of ORC Power Plants for Geothermal Application in Kenya by Combining Exergy and Pinch Point Analysis

Geothermal energy is a sustainable renewable source of energy. The installed capacity of geothermal energy in Kenya is 847.4 MWe of the total 2.7 GWe. This paper presents the effect of six different working fluids to optimize the geothermal of 21.5 MWe of reinjected brine at a single-flash power plant in Kenya. Engineering Equation Solver (EES) code was used to design and optimize simple organic Rankine (ORC) and regenerative cycles. The objective was to combine pinch point analysis and exergy analysis for the optimum utilization of geothermal energy by varying the turbine inlet pressure, pinch point, and reinjection temperature. The turbine inlet pressures, and pinch points were varied to obtain optimum pressures for higher net power output and exergy efficiencies. As the pressure increased, the efficiencies and net power generated increase to optimal at turbine inlet pressures between 2000 and 3000 kPa. By maintaining a condenser temperature at 46.7 °C, the turbine outlet pressures were 557.5 kPa for isobutene, 627.4 kPa for isobutane, 543.7 kPa for butene, 438.9 kPa for trans-2-butene, 412.3 kPa for R236ea, and 622.9 kPa for R142b. For the pinch point of 10 °C, the working fluid with a lower net power is trans-2-butene at 5936 kW for a flow rate of 138.8 kg/s and the highest reinjection at 89.05 °C. On the other hand, R236ae had a flow rate of 398.2 kg/s, a higher power output of 7273 kW, and the lowest reinjection temperature of 73.47 °C for a 5 °C pinch point. In the pinch point consideration, the suitable fluid will depend on the best reinjection temperatures. The pinch point affects the heat transfer rates and effectiveness in the heat exchangers. The best pinch point is 10 °C, since the reinjection temperatures are the highest between 83 and 89 °C. The analysis showed that for unlimited reinjection temperatures, basic ORC is suitable. The regenerative cycle would be best suited where reinjection temperature is constrained by brine geochemistry.

Forward Osmosis Absorption Heat Pumps for Space Conditioning and Graywater Purification: Cycle Development and Working Fluids Selection

A thermodynamic model is developed for a forward osmosis absorption heat pump capable of purifying graywater and providing year-round space conditioning with low-temperature heat as the primary energy input. The model is applied to 16 potential absorbents, and six are selected for parametric studies on desorber temperature, absorber temperature, condenser temperature, and heat sink temperature to determine the effects on the energy ratio (defined as the ratio of total useful output to total power input) of the cycle and the required graywater flow rate. Experiments are conducted to test the water flux and reverse solute flux in forward osmosis (FO) for most the promising absorbents. Of the six selected absorbents, four – two salt-organic mixtures and two pure salts – appear the most promising thermodynamically, while an ionic liquid demonstrates the best FO behavior.

Transfer of Ethanol and Aroma Compounds by Varying Specific Process Parameters in the Thermal Dealcoholisation of Beer

Dealcoholisation of beer has gained prominence over the last decade. A well-known procedure involves the combination of a rectification column for thermal dealcoholisation and a downstream column for aroma recovery. However, the recovery of valuable fermentation by-products is rarely performed due to limited data about the enrichment and depletion of ethanol and aromatic compounds. The influence of operating conditions on the transfer of ethanol and aroma compounds to the recovery fluid, henceforth, ‘aromawater’, has not yet been fully explored. Therefore, this study involved examining how ethanol concentration and aroma compounds in the aromawater are affected by the condenser temperature and reflux rate during thermal dealcoholisation. The aim was to obtain an aromawater having a maximum level of valuable aroma substances and a minimum level of ethanol for re-blending with non-alcoholic beer, hypothetically causing aroma intensification. An industrial system was used for sample production. Ethanol as well as higher alcohols and ester concentrations were analysed in the different material flows, and mass balances were thus compiled. Sensory analysis was performed to evaluate the beer aroma’s intensification as a sustainable industrial application. The obtained results indicate that increased condenser temperature was associated with increased aroma concentrations in the aromawater. If the temperature of the condenser’s coolant exceeded 15 °C, dealcoholisation < 0.05% abv could not be guaranteed. A higher reflux rate led to higher concentrations of fermentation by-products in the aromawater. Finally, the aroma profile of three non-alcoholic beers (0.0% abv, 0.5% abv after blending with original beer, and 0.5% abv after blending with aromawater) were evaluated. By blending, the attributes ‘estery’ and ‘flowery’ were assessed as dominant. The effect was more pronounced with aromawater than with the original beer.

Experimental Analysis of Refrigeration Ejector System by using Different Organic Refrigerants

This paper presents the experimental analysis performed on ejectors to optimize operating conditions like evaporator temperature, condenser temperature and generator temperature. Using the environmentally friendly working fluid R134a, R152a, R600a, R717 (Ammonia). Parametric analysis was performed to review the effect of blending chamber geometry on ejector performance which has direct impact on coefficient of performance of ejector refrigeration cycles. Results show that operating conditions and thus the effect of the deflection of the primary flow on the secondary flow is set. CFD simulations was performed to identify optimum geometry and optimum operating condition

Theoretical Analysis of a Single-Stage Gas-fired Ejector Heat Pump Water Heater

Ejector driven systems have the ability to operate at high efficiencies, utilizing recycled thermal energy as a power source. For a typical ejector heat pump system, the increase of the condenser temperature reduces the coefficient of performance (COP). In addition, if the condenser temperature is higher than the critical temperature, the ejector may not function. In this situation, the condenser temperature must be reduced, and an additional heater will be utilized to heat the production water from the condenser temperature to the desired temperature. In this investigation, a single-stage gas-fired ejector heat pump (EHP) is investigated and thermodynamically modeled in order to optimize the system COP for the purpose of heating water by utilizing the thermal energy from the ambient air. The effects of the high-temperature evaporator (HTE) and low-temperature evaporator (LTE) temperatures on the ejector critical back pressure and the EHP system performance are examined for a HTE temperature range of 120-180 °C and LTE temperatures of 15.5, 17.5, and 19.5 °C. Results show that an optimized COP of the EHP system exists which depends on HTE and LTE temperatures, primary nozzle throat diameters. In addition, it is found that the EHP COP is independent of the ejector COP. From this investigation a maximum EHP COP of 1.31 is able to be achieved for a HTE temperature of 160 °C and a LTE temperature of 19.5 °C with a total heating capacity of 15.98 kW.

Perbandingan Performa Refrigeran Propana dan Amonia pada Siklus Refrigerasi Dew Point Control Unit (DPCU)

Natural gas, that has been processed and met certain specifications, is sent to consumers through pipeline. Gas condensation within the pipeline should be avoided because it has negative impacts. Hydrocarbon dew point is a measure of the easiness of gas condensation. To meet the hydrocarbon dew point, heavy hydrocarbon should be extracted in dew point control unit (DPCU). The extraction is done by gas cooling in gas chiller followed by separating the liquid formed in low temperature separator (LTS). The gas chiller functions as an evaporator in the DPCU refrigeration cycle. Propane is a common refrigerant in the DPCU. In addition, ammonia is also a potential refrigerant due to its normal boiling point being close to the hydrocarbon dew point. Refrigeration cycle performance depends on evaporator temperature, condensor temperature, and the inherent pressure-enthalpy (PH) characteristic of the selected refrigerant. This study aimed to compare the performance from ammonia and propane against the change of evaporator and condenser temperature. This study was a dry research using Aspen Hysys V11.0 simulation software (academic license). The refrigeration cycle was a simple cycle with fixed variables in the form of evaporator load, saturated liquid at outlet condenser, and saturated vapour at outlet evaporator. This study indicated that at the same evaporator load, evaporator temperature, and condenser temperature, ammonia refrigeration cycle was better than the propane because coefficient of performance (COP) of ammonia was higher than propane. This study also modeled COP changes of propane and ammonia as mathematical equation. Quantitatively, it appeared that COP of propane was more sensitive than ammonia against both evaporator and condenser temperature changes.Keywords: ammonia; condenser; evaporator; propane; refrigeration cycle; simulationA B S T R A KGas alam yang telah diolah dan sesuai spesifikasinya dikirim ke konsumen melalui pipa. Kondensasi gas dalam pipa harus dihindari karena menimbulkan dampak negatif. Titik embun hidrokarbon menjadi ukuran kemudahan proses kondensasi gas. Untuk mencapai titik embun hidrokarbon yang diinginkan, maka hidrokarbon berat harus diekstraksi di dew point control unit (DPCU). Ekstraksi dilakukan dengan cara mendinginkan gas di gas chiller lalu memisahkan cairan yang terbentuk di low temperature separator (LTS). Gas chiller tersebut berfungsi sebagai evaporator pada siklus refrigerasi DPCU. Propana adalah refrigeran yang umum digunakan di DPCU. Selain itu, amonia juga menjadi refrigeran yang potensial karena kedekatan titik didih normalnya terhadap titik embun hidrokarbon yang diinginkan. Performa siklus refrigerasi dipengaruhi oleh temperatur evaporator, temperatur kondensor, dan karakteristik tekanan-entalpi (PH) yang melekat pada refrigeran yang dipilih. Penelitian ini bertujuan untuk membandingkan performa siklus refrigerasi propana dan amonia terhadap perubahan temperatur evaporator dan kondensor. Penelitian ini merupakan penelitian kering yang menggunakan perangkat lunak simulasi Aspen Hysys V11.0 (lisensi akademik). Siklus refrigerasi yang digunakan adalah simple cycle dengan variabel tetap berupa beban evaporator, kondisi cair jenuh outlet kondensor, dan kondisi uap jenuh outlet evaporator. Hasil penelitian ini menunjukkan bahwa pada beban evaporator, temperatur evaporator, dan temperatur kondensor yang sama, maka siklus refrigerasi amonia lebih baik dari propana karena COP amonia lebih tinggi dari propana. Penelitian ini juga memodelkan nilai COP propana dan amonia sebagai persamaan matematika. Secara kuantitatif, terlihat bahwa COP amonia lebih stabil dari propana terhadap perubahan temperatur evaporator dan kondensor.Kata kunci: amonia; evaporator; kondensor; propana; siklus refrigerasi; simulasi

Design of an Ejector Working in Combined Ejector - Vapor Compressor Refrigeration Cycle

In this paper, a calculation program is developed to design ejector working in a combined ejector – vapor compression refrigeration cycle. R134a is selected as the refrigerant for the ejector sub-cycle, and R410A is selected for the compressor sub-cycle. The effect of operating conditions and cooling capacity are examined. The results show that the area ratio increases with the increasing of generator temperature and intercooler temperature; and decreases with the increasing of condenser temperature and evaporator temperature. When the generator temperature, condenser temperature, intercooler temperature and evaporator temperature are 80°C, 34°C, 15°C, 0°C respectively, the area ratio is 8.55 and independent with cooling capacity. The design equations of significant dimensions based on operating conditions and cooling capacity are also introduced. The results show that R134a ejetor which is designed for simple ejector cycle is not suitable for combined cycle.

Creating Values from Biomass Pyrolysis in Sweden: Co-Production of H2, Biocarbon and Bio-Oil

Hydrogen and biocarbon are important materials for the future fossil-free metallurgical industries in Sweden; thus, it is interesting to investigate the process that can simultaneously produce both. Process simulations of biomass pyrolysis coupled with steam reforming and water-gas-shift to produce H2, biocarbon, and bio-oil are investigated in this work. The process simulation is performed based on a biomass pyrolysis plant currently operating in Sweden. Two co-production schemes are proposed: (1) production of biocarbon and H2, and (2) production of biocarbon, H2, and bio-oil. Sensitivity analysis is also performed to investigate the performance of the production schemes under different operating parameters. The results indicated that there are no notable differences in terms of the thermal efficiency for both cases. Varying the bio-oil condenser temperature only slightly changes the system’s thermal efficiency by less than 2%. On the other hand, an increase in biomass moisture content from 7 to 14 wt.% can decrease the system’s efficiency from 79.0% to 72.6%. Operating expenses are evaluated to elucidate the economics of 3 different cases: (1) no bio-oil production, (2) bio-oil production with the condenser at 50 °C, and (3) bio-oil production with the condenser at 130 °C. Based on operation expenses (OPEX) and revenue alone, it is found that producing more bio-oil helps improving the economics of the process. However, capital costs and the cost for post-processing of bio-oil should also be considered in the future. The estimated minimum selling price for biocarbon based on OPEX alone is approx. 10 SEK, which is within the range of the current commercial price of charcoal and coke.